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邮件协议rfc822文档

作者：知新_RL | 2024-07-12 21:40:44

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wimmail邮箱服务器是否支持rfc 822 headers选项

最近项目要解析eml文件，所以收藏以便以后查看 

  1. RFC #  822
  2. Obsoletes:  RFC #733  (NIC #41952)

RFC822: Standard for ARPA Internet Text Messages

Revised by David H. Crocker

Dept. of Electrical Engineering

University of Delaware, Newark, DE 19711

Network: DCrocker @ UDel-Relay

Partial Hypertext conversion by Tim Berners-Lee/CERN

TABLE OF CONTENTS 

  1. PREFACE ....................................................   ii
  2.  
  3. 1. INTRODUCTION ...........................................    1
  4.  
  5.     1.1.  Scope ............................................    1
  6.     1.2.  Communication Framework ..........................    2
  7.  
  8. 2. NOTATIONAL CONVENTIONS .................................    3
  9.  
  10. 3. LEXICAL ANALYSIS OF MESSAGES 3.1. General Description 3.2. Header Field Definitions 3.3. Lexical Tokens 3.4. Clarifications 4. MESSAGE SPECIFICATION ..................................   17
  11.  
  12.     4.1.  Syntax ...........................................   17
  13.     4.2.  Forwarding .......................................   19
  14.     4.3.  Trace Fields .....................................   20
  15.     4.4.  Originator Fields ................................   21
  16.     4.5.  Receiver Fields ..................................   23
  17.     4.6. Reference Fields .................................   23
  18.     4.7. Other Fields .....................................   24
  19.  
  20. 5. DATE AND TIME SPECIFICATION ............................   26
  21.  
  22.     5.1.  Syntax ...........................................   26
  23.     5.2.  Semantics ........................................   26
  24.  
  25. 6. ADDRESS SPECIFICATION ..................................   27
  26.  
  27.     6.1.  Syntax ...........................................   27
  28.     6.2.  Semantics ........................................   27
  29.     6.3.  Reserved Address .................................   33
  30.  
  31. 7. BIBLIOGRAPHY ...........................................   34
  32.  
  33.  
  34.                         APPENDIX
  35.  
  36. A. EXAMPLES ...............................................   36
  37. B. SIMPLE FIELD PARSING ...................................   40
  38. C. DIFFERENCES FROM RFC #733 ..............................   41
  39. D. ALPHABETICAL LISTING OF SYNTAX RULES ...................   44

PREFACE

By 1977, the Arpanet employed several informal standards for the text messages (mail) sent among its host computers. It was felt necessary to codify these practices and provide for those features that seemed imminent. The result of that effort was Request for Comments (RFC) #733, "Standard for the Format of ARPA Network Text Message", by Crocker, Vittal, Pogran, and Henderson. The specification attempted to avoid major changes in existing software, while permitting several new features.

This document revises the specifications in RFC #733, in order to serve the needs of the larger and more complex ARPA Internet. Some of RFC #733's features failed to gain adequate acceptance. In order to simplify the standard and the software that follows it, these features have been removed. A different addressing scheme is used, to handle the case of inter-network mail; and the concept of re-transmission has been introduced.

This specification is intended for use in the ARPA Internet. However, an attempt has been made to free it of any dependence on that environment, so that it can be applied to other network text message systems.

The specification of RFC #733 took place over the course of one year, using the ARPANET mail environment, itself, to provide an on-going forum for discussing the capabilities to be included. More than twenty individuals, from across the country, participated in the original discussion. The development of this revised specification has, similarly, utilized network mail-based group discussion. Both specification efforts greatly benefited from the comments and ideas of the participants.

The syntax of the standard, in RFC #733, was originally specified in the Backus-Naur Form (BNF) meta-language. Ken L. Harrenstien, of SRI International, was responsible for recoding the BNF into an augmented BNF that makes the representation smaller and easier to understand.

1. INTRODUCTION

1.1. SCOPE 

  1. This standard specifies a syntax for text messages that  are
  2. sent  among  computer  users, within the framework of "electronic
  3. mail".  The standard supersedes  the  one  specified  in  ARPANET
  4. Request  for Comments #733, "Standard for the Format of ARPA Net-
  5. work Text Messages".
  6.  
  7.      In this context, messages are viewed as having  an  envelope
  8. and  contents.   The  envelope  contains  whatever information is
  9. needed to accomplish transmission  and  delivery.   The  contents
  10. compose  the object to be delivered to the recipient.  This stan-
  11. dard applies only to the format and some of the semantics of mes-
  12. sage  contents.   It contains no specification of the information
  13. in the envelope.
  14.  
  15.      However, some message systems may use information  from  the
  16. contents  to create the envelope.  It is intended that this stan-
  17. dard facilitate the acquisition of such information by programs.
  18.  
  19.      Some message systems may  store  messages  in  formats  that
  20. differ  from the one specified in this standard.  This specifica-
  21. tion is intended strictly as a definition of what message content
  22. format is to be passed BETWEEN hosts.
  23.  
  24. Note:  This standard is NOT intended to dictate the internal for-
  25.        mats  used  by sites, the specific message system features
  26.        that they are expected to support, or any of  the  charac-
  27.        teristics  of  user interface programs that create or read
  28.        messages.
  29.  
  30.      A distinction should be made between what the  specification
  31. REQUIRES  and  what  it ALLOWS.  Messages can be made complex and
  32. rich with formally-structured components of information or can be
  33. kept small and simple, with a minimum of such information.  Also,
  34. the standard simplifies the interpretation  of  differing  visual
  35. formats  in  messages;  only  the  visual  aspect of a message is
  36. affected and not the interpretation  of  information  within  it.
  37. Implementors may choose to retain such visual distinctions.
  38.  
  39.      The formal definition is divided into four levels.  The bot-
  40. tom level describes the meta-notation used in this document.  The
  41. second level describes basic lexical analyzers that  feed  tokens
  42. to  higher-level  parsers.   Next is an overall specification for
  43. messages; it permits distinguishing individual fields.   Finally,
  44. there is definition of the contents of several structured fields.

1.2. COMMUNICATION FRAMEWORK 

  1. Messages consist of lines of text.   No  special  provisions
  2. are  made for encoding drawings, facsimile, speech, or structured
  3. text.  No significant consideration has been given  to  questions
  4. of  data  compression  or to transmission and storage efficiency,
  5. and the standard tends to be free with the number  of  bits  con-
  6. sumed.   For  example,  field  names  are specified as free text,
  7. rather than special terse codes.
  8.  
  9.      A general "memo" framework is used.  That is, a message con-
  10. sists of some information in a rigid format, followed by the main
  11. part of the message, with a format that is not specified in  this
  12. document.   The  syntax of several fields of the rigidly-formated
  13. ("headers") section is defined in  this  specification;  some  of
  14. these fields must be included in all messages.
  15.  
  16.      The syntax  that  distinguishes  between  header  fields  is
  17. specified  separately  from  the  internal  syntax for particular
  18. fields.  This separation is intended to allow simple  parsers  to
  19. operate on the general structure of messages, without concern for
  20. the detailed structure of individual header fields.   Appendix  B
  21. is provided to facilitate construction of these parsers.
  22.  
  23.      In addition to the fields specified in this document, it  is
  24. expected  that  other fields will gain common use.  As necessary,
  25. the specifications for these "extension-fields" will be published
  26. through  the same mechanism used to publish this document.  Users
  27. may also  wish  to  extend  the  set  of  fields  that  they  use
  28. privately.  Such "user-defined fields" are permitted.
  29.  
  30.      The framework severely constrains document tone and  appear-
  31. ance and is primarily useful for most intra-organization communi-
  32. cations and  well-structured   inter-organization  communication.
  33. It  also  can  be used for some types of inter-process communica-
  34. tion, such as simple file transfer and remote job entry.  A  more
  35. robust  framework might allow for multi-font, multi-color, multi-
  36. dimension encoding of information.  A  less  robust  one,  as  is
  37. present  in  most  single-machine  message  systems,  would  more
  38. severely constrain the ability to add fields and the decision  to
  39. include specific fields.  In contrast with paper-based communica-
  40. tion, it is interesting to note that the RECEIVER  of  a  message
  41. can   exercise  an  extraordinary  amount  of  control  over  the
  42. message's appearance.  The amount of actual control available  to
  43. message  receivers  is  contingent upon the capabilities of their
  44. individual message systems.

2. Notational Conventions

This specification uses an augmented Backus-Naur Form (BNF) notation. The differences from standard BNF involve naming rules and indicating repetition and "local" alternatives.

2.1. RULE NAMING 

  1. Angle brackets ("<", ">") are not  used,  in  general.   The
  2. name  of  a rule is simply the name itself, rather than "<name>".
  3. Quotation-marks enclose literal text (which may be  upper  and/or
  4. lower  case).   Certain  basic  rules  are  in uppercase, such as
  5. SPACE, TAB, CRLF, DIGIT, ALPHA, etc.  Angle brackets are used  in
  6. rule  definitions,  and  in  the rest of this  document, whenever
  7. their presence will facilitate discerning the use of rule names.

2.2. RULE1 / RULE2: ALTERNATIVES 

  1. Elements separated by slash ("/") are alternatives.   There-
  2. fore "foo / bar" will accept foo or bar.

2.3. (RULE1 RULE2): LOCAL ALTERNATIVES 

  1. Elements enclosed in parentheses are  treated  as  a  single
  2. element.   Thus,  "(elem  (foo  /  bar)  elem)"  allows the token
  3. sequences "elem foo elem" and "elem bar elem".

2.4. *RULE: REPETITION 

  1. The character "*" preceding an element indicates repetition.
  2. The full form is:
  3.  
  4.                          <l>*<m>element
  5.  
  6. indicating at least <l> and at most <m> occurrences  of  element.
  7. Default values are 0 and infinity so that "*(element)" allows any
  8. number, including zero; "1*element" requires at  least  one;  and
  9. "1*2element" allows one or two.

2.5. [RULE]: OPTIONAL 

  1. Square brackets enclose optional elements; "[foo  bar]"   is
  2. equivalent to "*1(foo bar)".

2.6. NRULE: SPECIFIC REPETITION 

  1. "<n>(element)" is equivalent to "<n>*<n>(element)"; that is,
  2. exactly  <n>  occurrences  of (element). Thus 2DIGIT is a 2-digit
  3. number, and 3ALPHA is a string of three alphabetic characters.

2.7. #RULE: LISTS 

  1. A construct "#" is defined, similar to "*", as follows:
  2.  
  3.                          <l>#<m>element
  4.  
  5. indicating at least <l> and at most <m> elements, each  separated
  6. by  one  or more commas (","). This makes the usual form of lists
  7. very easy; a rule such as '(element *("," element))' can be shown
  8. as  "1#element".   Wherever this construct is used, null elements
  9. are allowed, but do not  contribute  to  the  count  of  elements
  10. present.   That  is,  "(element),,(element)"  is  permitted,  but
  11. counts as only two elements.  Therefore, where at least one  ele-
  12. ment  is required, at least one non-null element must be present.
  13. Default values are 0 and infinity so that "#(element)" allows any
  14. number,  including  zero;  "1#element" requires at least one; and
  15. "1#2element" allows one or two.

2.8. ; COMMENTS 

  1. A semi-colon, set off some distance to  the  right  of  rule
  2. text,  starts  a comment that continues to the end of line.  This
  3. is a simple way of including useful notes in  parallel  with  the
  4. specifications.

3. LEXICAL ANALYSIS OF MESSAGES

3.1. GENERAL DESCRIPTION

A message consists of header fields and, optionally, a body. The body is simply a sequence of lines containing ASCII characters. It is separated from the headers by a null line (i.e., a line with nothing preceding the CRLF).

3.1.1. LONG HEADER FIELDS

Each header field can be viewed as a single, logical line of ASCII characters, comprising a field-name and a field-body. For convenience, the field-body portion of this conceptual entity can be split into a multiple-line representation; this is called "folding". The general rule is that wherever there may be linear-white-space (NOT simply LWSP-chars), a CRLF immediately followed by AT LEAST one LWSP-char may instead be inserted. Thus, the single line 
To:  "Joe & J. Harvey" <ddd @Org>, JJV @ BBN
can be represented as: 
  1. To:  "Joe & J. Harvey" <ddd @ Org>,
  2.                JJV@BBN
and 
  1. To:  "Joe & J. Harvey"
  2.                        <ddd@ Org>, JJV
  3.         @BBN
and 
  1. To:  "Joe &
  2.         J. Harvey" <ddd @ Org>, JJV @ BBN
The process of moving from this folded multiple-line representation of a header field to its single line representation is called "unfolding". Unfolding is accomplished by regarding CRLF immediately followed by a LWSP-char as equivalent to the LWSP-char.
Note:
While the standard permits folding wherever linear-white-space is permitted, it is recommended that structured fields, such as those containing addresses, limit folding to higher-level syntactic breaks. For address fields, it is recommended that such folding occur between addresses, after the separating comma.

3.1.2. STRUCTURE OF HEADER FIELDS

Once a field has been unfolded, it may be viewed as being composed of a field-name followed by a colon (":"), followed by a field-body, and terminated by a carriage-return/line-feed. The field-name must be composed of printable ASCII characters (i.e., characters that have values between 33. and 126., decimal, except colon). The field-body may be composed of any ASCII characters, except CR or LF. (While CR and/or LF may be present in the actual text, they are removed by the action of unfolding the field.)

Certain field-bodies of headers may be interpreted according to an internal syntax that some systems may wish to parse. These fields are called "structured fields". Examples include fields containing dates and addresses. Other fields, such as "Subject" and "Comments", are regarded simply as strings of text.

Note:
Any field which has a field-body that is defined as other than simply <text> is to be treated as a structured field.

Field-names, unstructured field bodies and structured field bodies each are scanned by their own, independent "lexical" analyzers.

3.1.3. UNSTRUCTURED FIELD BODIES

For some fields, such as "Subject" and "Comments", no structuring is assumed, and they are treated simply as <text>s, as in the message body. Rules of folding apply to these fields, so that such field bodies which occupy several lines must therefore have the second and successive lines indented by at least one LWSP-char.

3.1.4. STRUCTURED FIELD BODIES

To aid in the creation and reading of structured fields, the free insertion of linear-white-space (which permits folding by inclusion of CRLFs) is allowed between lexical tokens. Rather than obscuring the syntax specifications for these structured fields with explicit syntax for this linear-white-space, the existence of another "lexical" analyzer is assumed. This analyzer does not apply for unstructured field bodies that are simply strings of text, as described above. The analyzer provides an interpretation of the unfolded text composing the body of the field as a sequence of lexical symbols.

These symbols are:

  • individual special characters
  • quoted-strings
  • domain-literals
  • comments
  • atoms
The first four of these symbols are self-delimiting. Atoms are not; they are delimited by the self-delimiting symbols and by linear-white-space. For the purposes of regenerating sequences of atoms and quoted-strings, exactly one SPACE is assumed to exist, and should be used, between them. (Also, in the "Clarifications" section on "White Space", below, note the rules about treatment of multiple contiguous LWSP-chars.)

So, for example, the folded body of an address field 

  1. ":sysmail"@  Some-Group. Some-Org,
  2.        Muhammed.(I am  the greatest) Ali @(the)Vegas.WBA
is analyzed into the following lexical symbols and types: 
  1. :sysmail              quoted string
  2.                @                     special
  3.                Some-Group            atom
  4.                .                     special
  5.                Some-Org              atom
  6.                ,                     special
  7.                Muhammed              atom
  8.                .                     special
  9.                (I am  the greatest)  comment
  10.                Ali                   atom
  11.                @                     atom
  12.                (the)                 comment
  13.                Vegas                 atom
  14.                .                     special
  15.                WBA                   atom
The canonical representations for the data in these addresses are the following strings: 
  1. ":sysmail"@Some-Group.Some-Org
  2.  
  3.    and
  4.  
  5.                        Muhammed.Ali@Vegas.WBA
Note:
For purposes of display, and when passing such structured information to other systems, such as mail protocol services, there must be NO linear-white-space between <word>s that are separated by period (".") or at-sign ("@") and exactly one SPACE between all other <word>s. Also, headers should be in a folded form.

3.2. HEADER FIELD DEFINITIONS

These rules show a field meta-syntax, without regard for the particular type or internal syntax. Their purpose is to permit detection of fields; also, they present to higher-level parsers an image of each field as fitting on one line. 
  1. field       =  field-name ":" [ field-body ] CRLF
  2.  
  3. field-name  =  1*<any CHAR, excluding CTLs, SPACE, and ":">
  4.  
  5. field-body  =  field-body-contents
  6.                [CRLF LWSP-char field-body]
  7.  
  8. field-body-contents =
  9.               <the ASCII characters making up the field-body, as
  10.                defined in the following sections, and consisting
  11.                of combinations of atom, quoted-string, and
  12.                specials tokens, or else consisting of texts>

3.3. LEXICAL TOKENS

The following rules are used to define an underlying lexical analyzer, which feeds tokens to higher level parsers. See the ANSI references, in the Bibliography. 
  1. ; (  Octal, Decimal.)
  2. CHAR        =  <any ASCII character>        ; (  0-177,  0.-127.)
  3. ALPHA       =  <any ASCII alphabetic character>
  4.                                             ; (101-132, 65.- 90.)
  5.                                             ; (141-172, 97.-122.)
  6. DIGIT       =  <any ASCII decimal digit>    ; ( 60- 71, 48.- 57.)
  7. CTL         =  <any ASCII control           ; (  0- 37,  0.- 31.)
  8.                 character and DEL>          ; (    177,     127.)
  9. CR          =  <ASCII CR, carriage return>  ; (     15,      13.)
  10. LF          =  <ASCII LF, linefeed>         ; (     12,      10.)
  11. SPACE       =  <ASCII SP, space>            ; (     40,      32.)
  12. HTAB        =  <ASCII HT, horizontal-tab>   ; (     11,       9.)
  13. <">         =  <ASCII quote mark>           ; (     42,      34.)
  14. CRLF        =  CR LF
  16. LWSP-char   =  SPACE / HTAB                 ; semantics = SPACE
  18. linear-white-space =  1*([CRLF] LWSP-char)  ; semantics = SPACE
  19.                                             ; CRLF => folding
  21. specials    =  "(" / ")" / "<" / ">" / "@"  ; Must be in quoted-
  22.             /  "," / ";" / ":" / "\" / <">  ;  string, to use
  23.             /  "." / "[" / "]"              ;  within a word.
  24.  
  25. delimiters  =  specials / linear-white-space / comment
  26.  
  27. text        =  <any CHAR, including bare    ; => atoms, specials,
  28.                 CR & bare LF, but NOT       ;  comments and
  29.                 including CRLF>             ;  quoted-strings are
  30.                                             ;  NOT recognized. atom =  1*<any CHAR except specials, SPACE and CTLs>
  31.  
  32. quoted-string = <"> *(qtext/quoted-pair) <">; Regular qtext or
  33.                                             ;   quoted chars.
  34.  
  35. qtext       =  <any CHAR excepting <">,     ; => may be folded
  36.                 "\" & CR, and including
  37.                 linear-white-space>
  39. domain-literal =  "[" *(dtext / quoted-pair) "]"
  45. dtext       =  <any CHAR excluding "[",     ; => may be folded
  46.                 "]", "\" & CR, & including
  47.                 linear-white-space>
  49. comment     =  "(" *(ctext / quoted-pair / comment) ")"
  51. ctext       =  <any CHAR excluding "(",     ; => may be folded
  52.                 ")", "\" & CR, & including
  53.                 linear-white-space>
  55. quoted-pair =  "\" CHAR                     ; may quote any char
  57. phrase      =  1*word                       ; Sequence of words word =  atom / quoted-string

3.4. CLARIFICATIONS

3.4.1. QUOTING

Some characters are reserved for special interpretation, such as delimiting lexical tokens. To permit use of these characters as uninterpreted data, a quoting mechanism is provided. To quote a character, precede it with a backslash ("\").

This mechanism is not fully general. Characters may be quoted only within a subset of the lexical constructs. In particular, quoting is limited to use within:

  • - quoted-string
  • - domain-literal
  • - comment
Within these constructs, quoting is REQUIRED for CR and "\" and for the character(s) that delimit the token (e.g., "(" and ")" for a comment). However, quoting is PERMITTED for any character.
Note:
In particular, quoting is NOT permitted within atoms. For example when the local-part of an addr-spec must contain a special character, a quoted string must be used. Therefore, a specification such as: 
Full\ Name@Domain
is not legal and must be specified as: 
"Full Name"@Domain

3.4.2. WHITE SPACE 

  1. Note:  In structured field bodies, multiple linear space ASCII
  2.           characters  (namely  HTABs  and  SPACEs) are treated as
  3.           single spaces and may freely surround any  symbol.   In
  4.           all header fields, the only place in which at least one
  5.           LWSP-char is REQUIRED is at the beginning of  continua-
  6.           tion lines in a folded field.
  7.  
  8.    When passing text to processes  that  do  not  interpret  text
  9.    according to this standard (e.g., mail protocol servers), then
  10.    NO linear-white-space characters should occur between a period
  11.    (".") or at-sign ("@") and a <word>.  Exactly ONE SPACE should
  12.    be used in place of arbitrary linear-white-space  and  comment
  13.    sequences.
  14.  
  15.    Note:  Within systems conforming to this standard, wherever  a
  16.           member of the list of delimiters is allowed, LWSP-chars
  17.           may also occur before and/or after it.
  18.  
  19.    Writers of  mail-sending  (i.e.,  header-generating)  programs
  20.    should realize that there is no network-wide definition of the
  21.    effect of ASCII HT (horizontal-tab) characters on the  appear-
  22.    ance  of  text  at another network host; therefore, the use of
  23.    tabs in message headers, though permitted, is discouraged.

3.4.3. COMMENTS 

  1. A comment is a set of ASCII characters, which is  enclosed  in
  2.    matching  parentheses  and which is not within a quoted-string
  3.    The comment construct permits message originators to add  text
  4.    which  will  be  useful  for  human readers, but which will be
  5.    ignored by the formal semantics.  Comments should be  retained
  6.    while  the  message  is subject to interpretation according to
  7.    this standard.  However, comments  must  NOT  be  included  in
  8.    other  cases,  such  as  during  protocol  exchanges with mail
  9.    servers.
  10.  
  11.    Comments nest, so that if an unquoted left parenthesis  occurs
  12.    in  a  comment  string,  there  must  also be a matching right
  13.    parenthesis.  When a comment acts as the delimiter  between  a
  14.    sequence of two lexical symbols, such as two atoms, it is lex-
  15.    ically equivalent with a single SPACE,  for  the  purposes  of
  16.    regenerating  the  sequence, such as when passing the sequence
  17.    onto a mail protocol server.  Comments are  detected  as  such
  18.    only within field-bodies of structured fields.
  19.  
  20.    If a comment is to be "folded" onto multiple lines,  then  the
  21.    syntax  for  folding  must  be  adhered to.  (See the "Lexical
  22.    Analysis of Messages" section on "Folding Long Header  Fields"
  23.    above,  and  the  section on "Case Independence" below.)  Note
  24.    that  the  official  semantics  therefore  do  not  "see"  any
  25.    unquoted CRLFs that are in comments, although particular pars-
  26.    ing programs may wish to note their presence.  For these  pro-
  27.    grams,  it would be reasonable to interpret a "CRLF LWSP-char"
  28.    as being a CRLF that is part of the comment; i.e., the CRLF is
  29.    kept  and  the  LWSP-char is discarded.  Quoted CRLFs (i.e., a
  30.    backslash followed by a CR followed by a  LF)  still  must  be
  31.    followed by at least one LWSP-char.
  32.  
  33. 3.4.4.  DELIMITING AND QUOTING CHARACTERS
  34.  
  35.    The quote character (backslash) and  characters  that  delimit
  36.    syntactic  units  are not, generally, to be taken as data that
  37.    are part of the delimited or quoted unit(s).   In  particular,
  38.    the   quotation-marks   that   define   a  quoted-string,  the
  39.    parentheses that define  a  comment  and  the  backslash  that
  40.    quotes  a  following  character  are  NOT  part of the quoted-
  41.    string, comment or quoted character.  A quotation-mark that is
  42.    to  be  part  of  a quoted-string, a parenthesis that is to be
  43.    part of a comment and a backslash that is to be part of either
  44.    must  each be preceded by the quote-character backslash ("\").
  45.    Note that the syntax allows any character to be quoted  within
  46.    a  quoted-string  or  comment; however only certain characters
  47.    MUST be quoted to be included as data.  These  characters  are
  48.    the  ones that are not part of the alternate text group (i.e.,
  49.    ctext or qtext).
  50.  
  51.    The one exception to this rule  is  that  a  single  SPACE  is
  52.    assumed  to  exist  between  contiguous words in a phrase, and
  53.    this interpretation is independent of  the  actual  number  of
  54.    LWSP-chars  that  the  creator  places  between the words.  To
  55.    include more than one SPACE, the creator must make  the  LWSP-
  56.    chars be part of a quoted-string.
  57.  
  58.    Quotation marks that delimit a quoted string  and  backslashes
  59.    that  quote  the  following character should NOT accompany the
  60.    quoted-string when the string is passed to processes  that  do
  61.    not interpret data according to this specification (e.g., mail
  62.    protocol servers).
  63.  
  64. 3.4.5.  QUOTED-STRINGS
  65.  
  66.    Where permitted (i.e., in words in structured fields)  quoted-
  67.    strings  are  treated  as a single symbol.  That is, a quoted-
  68.    string is equivalent to an atom, syntactically.  If a  quoted-
  69.    string  is to be "folded" onto multiple lines, then the syntax
  70.    for folding must be adhered to.  (See the "Lexical Analysis of
  74.    Messages"  section  on "Folding Long Header Fields" above, and
  75.    the section on "Case  Independence"  below.)   Therefore,  the
  76.    official  semantics  do  not  "see" any bare CRLFs that are in
  77.    quoted-strings; however particular parsing programs  may  wish
  78.    to  note  their presence.  For such programs, it would be rea-
  79.    sonable to interpret a "CRLF LWSP-char" as being a CRLF  which
  80.    is  part  of the quoted-string; i.e., the CRLF is kept and the
  81.    LWSP-char is discarded.  Quoted CRLFs (i.e., a backslash  fol-
  82.    lowed  by  a CR followed by a LF) are also subject to rules of
  83.    folding, but the presence of the quoting character (backslash)
  84.    explicitly  indicates  that  the  CRLF  is  data to the quoted
  85.    string.  Stripping off the first following LWSP-char  is  also
  86.    appropriate when parsing quoted CRLFs.

3.4.6. BRACKETING CHARACTERS 

  1. There is one type of bracket which must occur in matched pairs
  2.    and may have pairs nested within each other:
  3.  
  4.        o   Parentheses ("(" and ")") are used  to  indicate  com-
  5.            ments.
  6.  
  7.    There are three types of brackets which must occur in  matched
  8.    pairs, and which may NOT be nested:
  9.  
  10.        o   Colon/semi-colon (":" and ";") are   used  in  address
  11.            specifications  to  indicate that the included list of
  12.            addresses are to be treated as a group.
  13.  
  14.        o   Angle brackets ("<" and ">")  are  generally  used  to
  15.            indicate  the  presence of a one machine-usable refer-
  16.            ence (e.g., delimiting mailboxes), possibly  including
  17.            source-routing to the machine.
  18.  
  19.        o   Square brackets ("[" and "]") are used to indicate the
  20.            presence  of  a  domain-literal, which the appropriate
  21.            name-domain  is  to  use  directly,  bypassing  normal
  22.            name-resolution mechanisms.

3.4.7. CASE INDEPENDENCE

Except as noted, alphabetic strings may be represented in any combination of upper and lower case. The only syntactic units which requires preservation of case information are:
  • text
  • qtext
  • dtext
  • ctext
  • quoted-pair
  • local-part, except "Postmaster" 
  1. When matching any other syntactic unit, case is to be ignored.
  2.    For  example, the field-names "From", "FROM", "from", and even
  3.    "FroM" are semantically equal and should all be treated ident-
  4.    ically.
  5.  
  6.    When generating these units, any mix of upper and  lower  case
  7.    alphabetic  characters  may  be  used.  The case shown in this
  8.    specification is suggested for message-creating processes.
  9.  
  10.    Note:  The reserved local-part address unit, "Postmaster",  is
  11.           an  exception.   When  the  value "Postmaster" is being
  12.           interpreted, it must be  accepted  in  any  mixture  of
  13.           case, including "POSTMASTER", and "postmaster".
  14.  
  15. 3.4.8.  FOLDING LONG HEADER FIELDS
  16.  
  17.    Each header field may be represented on exactly one line  con-
  18.    sisting  of the name of the field and its body, and terminated
  19.    by a CRLF; this is what the parser sees.  For readability, the
  20.    field-body  portion of long header fields may be "folded" onto
  21.    multiple lines of the actual field.  "Long" is commonly inter-
  22.    preted  to  mean greater than 65 or 72 characters.  The former
  23.    length serves as a limit, when the message is to be viewed  on
  24.    most  simple terminals which use simple display software; how-
  25.    ever, the limit is not imposed by this standard.
  26.  
  27.    Note:  Some display software often can selectively fold lines,
  28.           to  suit  the display terminal.  In such cases, sender-
  29.           provided  folding  can  interfere  with   the   display
  30.           software.
  31.  
  32. 3.4.9.  BACKSPACE CHARACTERS
  33.  
  34.    ASCII BS characters (Backspace, decimal 8) may be included  in
  35.    texts and quoted-strings to effect overstriking.  However, any
  36.    use of backspaces which effects an overstrike to the  left  of
  37.    the beginning of the text or quoted-string is prohibited.

3.4.10. NETWORK-SPECIFIC TRANSFORMATIONS 

  1. During transmission through heterogeneous networks, it may  be
  2.    necessary  to  force data to conform to a network's local con-
  3.    ventions.  For example, it may be required that a CR  be  fol-
  4.    lowed  either by LF, making a CRLF, or by <null>, if the CR is
  5.    to stand alone).  Such transformations are reversed, when  the
  6.    message exits that network.
  7.  
  8.    When  crossing  network  boundaries,  the  message  should  be
  9.    treated  as  passing  through  two modules.  It will enter the
  10.    first module containing whatever network-specific  transforma-
  11.    tions  that  were  necessary  to  permit migration through the
  12.    "current" network.  It then passes through the modules:
Transformation ReversalThe "current" network's idiosyncracies are removed and the message is returned to the canonical form specified in this standard.TransformationThe "next" network's local idiosyncracies are imposed on the message. 
  1. ------------------
  2.                From   ==>  | Remove Net-A   |
  3.                Net-A       | idiosyncracies |
  4.                            ------------------
  5.                                   ||
  6.                                   \/
  7.                              Conformance
  8.                              with standard
  9.                                   ||
  10.                                   \/
  11.                            ------------------
  12.                            | Impose Net-B   |  ==>  To
  13.                            | idiosyncracies |       Net-B
  14.                            ------------------

4. Message Specification

4.1. SYNTAX 

  1. Note:  Due to an artifact of the notational conventions, the syn-
  2.        tax  indicates that, when present, some fields, must be in
  3.        a particular order.  Header fields  are  NOT  required  to
  4.        occur  in  any  particular  order, except that the message
  5.        body must occur AFTER  the  headers.   It  is  recommended
  6.        that,  if  present,  headers be sent in the order "Return-
  7.        Path", "Received", "Date",  "From",  "Subject",  "Sender",
  8.        "To", "cc", etc.
  9.  
  10.        This specification permits multiple  occurrences  of  most
  11.        fields.   Except  as  noted,  their  interpretation is not
  12.        specified here, and their use is discouraged.
  13.  
  14.      The following syntax for the bodies of various fields should
  15. be  thought  of  as  describing  each field body as a single long
  16. string (or line).  The "Lexical Analysis of Message"  section  on
  17. "Long  Header Fields", above, indicates how such long strings can
  18. be represented on more than one line in  the  actual  transmitted
  19. message.
  20.  
  21. message     =  fields *( CRLF *text )       ; Everything after
  22.                                             ;  first null line
  23.                                             ;  is message body
  24.  
  25. fields      =    dates                      ; Creation time,
  26.                  source                     ;  author id & one
  27.                1*destination                ;  address required
  28.                 *optional-field             ;  others optional
  29.  
  30. source      = [  trace ]                    ; net traversals
  31.                  originator                 ; original mail
  32.               [  resent ]                   ; forwarded
  33.  
  34. trace       =    return                     ; path to sender
  35.                1*received                   ; receipt tags
  36.  
  37. return      =  "Return-path" ":" route-addr ; return address
  38.  
  39. received    =  "Received"    ":"            ; one per relay
  40.                   ["from" domain]           ; sending host
  41.                   ["by"   domain]           ; receiving host
  42.                   ["via"  atom]             ; physical path
  43.                  *("with" atom)             ; link/mail protocol
  44.                   ["id"   msg-id]           ; receiver msg id
  45.                   ["for"  addr-spec]        ; initial form
  46.  
  47.  
  48.  
  49.                    ";"    date-time         ; time received
  50.  
  51. originator  =   authentic                   ; authenticated addr
  52.               [ "Reply-To"   ":" 1#address] )
  53.  
  54. authentic   =   "From"       ":"   mailbox  ; Single author
  55.             / ( "Sender"     ":"   mailbox  ; Actual submittor
  56.                 "From"       ":" 1#mailbox) ; Multiple authors
  57.                                             ;  or not sender
  58.  
  59. resent      =   resent-authentic
  60.               [ "Resent-Reply-To"  ":" 1#address] )
  61.  
  62. resent-authentic =
  63.             =   "Resent-From"      ":"   mailbox
  64.             / ( "Resent-Sender"    ":"   mailbox
  65.                 "Resent-From"      ":" 1#mailbox  )
  66.  
  67. dates       =   orig-date                   ; Original
  68.               [ resent-date ]               ; Forwarded
  69.  
  70. orig-date   =  "Date"        ":"   date-time
  71.  
  72. resent-date =  "Resent-Date" ":"   date-time
  73.  
  74. destination =  "To"          ":" 1#address  ; Primary
  75.             /  "Resent-To"   ":" 1#address
  76.             /  "cc"          ":" 1#address  ; Secondary
  77.             /  "Resent-cc"   ":" 1#address
  78.             /  "bcc"         ":"  #address  ; Blind carbon
  79.             /  "Resent-bcc"  ":"  #address
  80.  
  81. optional-field =
  82.             /  "Message-ID"        ":"   msg-id
  83.             /  "Resent-Message-ID" ":"   msg-id
  84.             /  "In-Reply-To"       ":"  *(phrase / msg-id)
  85.             /  "References"        ":"  *(phrase / msg-id)
  86.             /  "Keywords"          ":"  #phrase
  87.             /  "Subject"           ":"  *text
  88.             /  "Comments"          ":"  *text
  89.             /  "Encrypted"         ":" 1#2word
  90.             /  extension-field              ; To be defined
  91.             /  user-defined-field           ; May be pre-empted msg-id =  "<" addr-spec ">"            ; Unique message id
  92.  
  93.  
  94.  
  95.  
  96.  
  97.  
  98.  
  99. extension-field =
  100.               <Any field which is defined in a document
  101.                published as a formal extension to this
  102.                specification; none will have names beginning
  103.                with the string "X-">
  104.  
  105. user-defined-field =
  106.               <Any field which has not been defined
  107.                in this specification or published as an
  108.                extension to this specification; names for
  109.                such fields must be unique and may be
  110.                pre-empted by published extensions>

4.2. FORWARDING 

  1. Some systems permit mail recipients to  forward  a  message,
  2. retaining  the original headers, by adding some new fields.  This
  3. standard supports such a service, through the "Resent-" prefix to
  4. field names.
  5.  
  6.      Whenever the string "Resent-" begins a field name, the field
  7. has  the  same  semantics as a field whose name does not have the
  8. prefix.  However, the message is assumed to have  been  forwarded
  9. by  an original recipient who attached the "Resent-" field.  This
  10. new field is treated as being more recent  than  the  equivalent,
  11. original  field.   For  example, the "Resent-From", indicates the
  12. person that forwarded the message, whereas the "From" field indi-
  13. cates the original author.
  14.  
  15.      Use of such precedence  information  depends  upon  partici-
  16. pants'  communication needs.  For example, this standard does not
  17. dictate when a "Resent-From:" address should receive replies,  in
  18. lieu of sending them to the "From:" address.
  19.  
  20. Note:  In general, the "Resent-" fields should be treated as con-
  21.        taining  a  set  of information that is independent of the
  22.        set of original fields.  Information for  one  set  should
  23.        not  automatically be taken from the other.  The interpre-
  24.        tation of multiple "Resent-" fields, of the same type,  is
  25.        undefined.
In the remainder of this specification, occurrence of legal "Resent-" fields are treated identically with the occurrence of fields whose names do not contain this prefix.

4.3. TRACE FIELDS

Trace information is used to provide an audit trail of message handling. In addition, it indicates a route back to the sender of the message.

The list of known "via" and "with" values are registered with the Network Information Center, SRI International, Menlo Park, California.

4.3.1. RETURN-PATH 

  1. This field  is  added  by  the  final  transport  system  that
  2.    delivers  the message to its recipient.  The field is intended
  3.    to contain definitive information about the address and  route
  4.    back to the message's originator.
  5.  
  6.    Note:  The "Reply-To" field is added  by  the  originator  and
  7.           serves  to  direct  replies,  whereas the "Return-Path"
  8.           field is used to identify a path back to  the  origina-
  9.           tor.
  10.  
  11.    While the syntax  indicates  that  a  route  specification  is
  12.    optional,  every attempt should be made to provide that infor-
  13.    mation in this field.

4.3.2. RECEIVED 

  1. A copy of this field is added by each transport  service  that
  2.    relays the message.  The information in the field can be quite
  3.    useful for tracing transport problems.
  4.  
  5.    The names of the sending  and  receiving  hosts  and  time-of-
  6.    receipt may be specified.  The "via" parameter may be used, to
  7.    indicate what physical mechanism the message  was  sent  over,
  8.    such  as  Arpanet or Phonenet, and the "with" parameter may be
  9.    used to indicate the mail-,  or  connection-,  level  protocol
  10.    that  was  used, such as the SMTP mail protocol, or X.25 tran-
  11.    sport protocol.
  12.  
  13.    Note:  Several "with" parameters may  be  included,  to  fully
  14.           specify the set of protocols that were used.
  15.  
  16.    Some transport services queue mail; the internal message iden-
  17.    tifier that is assigned to the message may be noted, using the
  18.    "id" parameter.  When the  sending  host  uses  a  destination
  19.    address specification that the receiving host reinterprets, by
  20.  
  21.  
  22.  
  23.    expansion or transformation, the receiving host  may  wish  to
  24.    record  the original specification, using the "for" parameter.
  25.    For example, when a copy of mail is sent to the  member  of  a
  26.    distribution  list,  this  parameter may be used to record the
  27.    original address that was used to specify the list.

4.4. ORIGINATOR FIELDS 

  1. The standard allows only a subset of the combinations possi-
  2. ble  with the From, Sender, Reply-To, Resent-From, Resent-Sender,
  3. and Resent-Reply-To fields.  The limitation is intentional.

4.4.1. FROM / RESENT-FROM 

  1. This field contains the identity of the person(s)  who  wished
  2.    this  message to be sent.  The message-creation process should
  3.    default this field  to  be  a  single,  authenticated  machine
  4.    address,  indicating  the  AGENT  (person,  system or process)
  5.    entering the message.  If this is not done, the "Sender" field
  6.    MUST  be  present.  If the "From" field IS defaulted this way,
  7.    the "Sender" field is  optional  and  is  redundant  with  the
  8.    "From"  field.   In  all  cases, addresses in the "From" field
  9.    must be machine-usable (addr-specs) and may not contain  named
  10.    lists (groups).

4.4.2. SENDER / RESENT-SENDER 

  1. This field contains the authenticated identity  of  the  AGENT
  2.    (person,  system  or  process)  that sends the message.  It is
  3.    intended for use when the sender is not the author of the mes-
  4.    sage,  or  to  indicate  who among a group of authors actually
  5.    sent the message.  If the contents of the "Sender" field would
  6.    be  completely  redundant  with  the  "From"  field,  then the
  7.    "Sender" field need not be present and its use is  discouraged
  8.    (though  still legal).  In particular, the "Sender" field MUST
  9.    be present if it is NOT the same as the "From" Field.
  10.  
  11.    The Sender mailbox  specification  includes  a  word  sequence
  12.    which  must correspond to a specific agent (i.e., a human user
  13.    or a computer program) rather than a standard  address.   This
  14.    indicates  the  expectation  that  the field will identify the
  15.    single AGENT (person,  system,  or  process)  responsible  for
  16.    sending  the mail and not simply include the name of a mailbox
  17.    from which the mail was sent.  For example in the  case  of  a
  18.    shared login name, the name, by itself, would not be adequate.
  19.    The local-part address unit, which refers to  this  agent,  is
  20.    expected to be a computer system term, and not (for example) a
  21.    generalized person reference which can  be  used  outside  the
  22.    network text message context.
  23.  
  24.  
  25.  
  26.    Since the critical function served by the  "Sender"  field  is
  27.    identification  of  the agent responsible for sending mail and
  28.    since computer programs cannot be held accountable  for  their
  29.    behavior, it is strongly recommended that when a computer pro-
  30.    gram generates a message, the HUMAN  who  is  responsible  for
  31.    that program be referenced as part of the "Sender" field mail-
  32.    box specification.

4.4.3. REPLY-TO / RESENT-REPLY-TO 

  1. This field provides a general  mechanism  for  indicating  any
  2.    mailbox(es)  to which responses are to be sent.  Three typical
  3.    uses for this feature can  be  distinguished.   In  the  first
  4.    case,  the  author(s) may not have regular machine-based mail-
  5.    boxes and therefore wish(es) to indicate an alternate  machine
  6.    address.   In  the  second case, an author may wish additional
  7.    persons to be made aware of, or responsible for,  replies.   A
  8.    somewhat  different  use  may be of some help to "text message
  9.    teleconferencing" groups equipped with automatic  distribution
  10.    services:   include the address of that service in the "Reply-
  11.    To" field of all messages  submitted  to  the  teleconference;
  12.    then  participants  can  "reply"  to conference submissions to
  13.    guarantee the correct distribution of any submission of  their
  14.    own.
  15.  
  16.    Note:  The "Return-Path" field is added by the mail  transport
  17.           service,  at the time of final deliver.  It is intended
  18.           to identify a path back to the orginator  of  the  mes-
  19.           sage.   The  "Reply-To"  field  is added by the message
  20.           originator and is intended to direct replies.
  21.  
  22. 4.4.4.  AUTOMATIC USE OF FROM / SENDER / REPLY-TO
  23.  
  24.    For systems which automatically  generate  address  lists  for
  25.    replies to messages, the following recommendations are made:
  26.  
  27.        o   The "Sender" field mailbox should be sent  notices  of
  28.            any  problems in transport or delivery of the original
  29.            messages.  If there is no  "Sender"  field,  then  the
  30.            "From" field mailbox should be used.
  31.  
  32.        o   The  "Sender"  field  mailbox  should  NEVER  be  used
  33.            automatically, in a recipient's reply message.
  35.        o   If the "Reply-To" field exists, then the reply  should
  36.            go to the addresses indicated in that field and not to
  37.            the address(es) indicated in the "From" field.
  43.        o   If there is a "From" field, but no  "Reply-To"  field,
  44.            the  reply should be sent to the address(es) indicated
  45.            in the "From" field.
  47.    Sometimes, a recipient may actually wish to  communicate  with
  48.    the  person  that  initiated  the  message  transfer.  In such
  49.    cases, it is reasonable to use the "Sender" address.
  51.    This recommendation is intended  only  for  automated  use  of
  52.    originator-fields  and is not intended to suggest that replies
  53.    may not also be sent to other recipients of messages.   It  is
  54.    up  to  the  respective  mail-handling programs to decide what
  55.    additional facilities will be provided.
  57.    Examples are provided in Appendix A.
  59. 4.5.  RECEIVER FIELDS
  61. 4.5.1.  TO / RESENT-TO
  63.    This field contains the identity of the primary recipients  of
  64.    the message.
  66. 4.5.2.  CC / RESENT-CC
  68.    This field contains the identity of  the  secondary  (informa-
  69.    tional) recipients of the message.
  71. 4.5.3.  BCC / RESENT-BCC
  73.    This field contains the identity of additional  recipients  of
  74.    the  message.   The contents of this field are not included in
  75.    copies of the message sent to the primary and secondary  reci-
  76.    pients.   Some  systems  may choose to include the text of the
  77.    "Bcc" field only in the author(s)'s  copy,  while  others  may
  78.    also include it in the text sent to all those indicated in the
  79.    "Bcc" list.

4.6. REFERENCE FIELDS

4.6.1. Message-ID / Resent-Message-ID

This field contains a  unique identifier  (the local-part address unit) which refers to THIS version of THIS message. The uniqueness of the message identifier is guaranteed by the host which generates it. This identifier is intended to be machine readable and not necessarily meaningful to humans. A message identifier pertains to exactly one instantiation of a particular message; subsequent revisions to the message should each receive new message identifiers.

4.6.2. IN-REPLY-TO

The contents of this field identify previous correspondence which this message answers. Note that if message identifiers are used in this field, they must use the  msg-id specification format.

4.6.3. REFERENCES

The contents of this field identify other correspondence which this message references. Note that if message identifiers are used, they must use the  msg-id  specification format.

4.6.4. KEYWORDS

This field contains keywords or phrases, separated by commas.

4.7. Other Fields

4.7.1. SUBJECT

This is intended to provide a summary, or indicate the nature, of the message.

4.7.2. COMMENTS

Permits adding text comments onto the message without disturbing the contents of the message's body.

4.7.3. ENCRYPTED 

  1. Sometimes,  data  encryption  is  used  to  increase  the
  2.    privacy  of  message  contents.   If the body of a message has
  3.    been encrypted, to keep its contents private, the  "Encrypted"
  4.    field  can be used to note the fact and to indicate the nature
  5.    of the encryption.  The first <word> parameter  indicates  the
  6.    software  used  to  encrypt the body, and the second, optional
  7.    <word> is intended to  aid  the  recipient  in  selecting  the
  8.    proper  decryption  key.   This  code word may be viewed as an
  9.    index to a table of keys held by the recipient.
  10.  
  11.    Note:  Unfortunately, headers must contain envelope,  as  well
  12.           as  contents,  information.  Consequently, it is neces-
  13.           sary that they remain unencrypted, so that  mail  tran-
  14.           sport   services   may   access   them.   Since  names,
  15.           addresses, and "Subject"  field  contents  may  contain
  16.  
  17.  
  18.  
  19.           sensitive  information,  this  requirement limits total
  20.           message privacy.
  21.  
  22.         Names of encryption software are registered with the Net-
  23.    work  Information Center, SRI International, Menlo Park, Cali-
  24.    fornia.

4.7.4. EXTENSION-FIELD 

  1. A limited number of common fields have  been  defined  in
  2.    this  document.   As  network mail requirements dictate, addi-
  3.    tional fields may be standardized.   To  provide  user-defined
  4.    fields  with  a  measure  of  safety,  in name selection, such
  5.    extension-fields will never have names  that  begin  with  the
  6.    string "X-".
  7.  
  8.         Names of Extension-fields are registered with the Network
  9.    Information Center, SRI International, Menlo Park, California.

4.7.5. USER-DEFINED-FIELD 

  1. Individual users of network mail are free to  define  and
  2.    use  additional  header  fields.   Such fields must have names
  3.    which are not already used in the current specification or  in
  4.    any definitions of extension-fields, and the overall syntax of
  5.    these user-defined-fields must conform to this specification's
  6.    rules   for   delimiting  and  folding  fields.   Due  to  the
  7.    extension-field  publishing  process,  the  name  of  a  user-
  8.    defined-field may be pre-empted
  9.  
  10.    Note:  The prefatory string "X-" will never  be  used  in  the
  11.           names  of Extension-fields.  This provides user-defined
  12.           fields with a protected set of names.

5. Date and Time Specification

5.1. SYNTAX 

  1. date-time   =  [ day "," ] date time        ; dd mm yy
  2.                                             ;  hh:mm:ss zzz
  3.  
  4. day         =  "Mon"  / "Tue" /  "Wed"  / "Thu"
  5.             /  "Fri"  / "Sat" /  "Sun"
  6.  
  7. date        =  1*2DIGIT month 2DIGIT        ; day month year
  8.                                             ;  e.g. 20 Jun 82
  9.  
  10. month       =  "Jan"  /  "Feb" /  "Mar"  /  "Apr"
  11.             /  "May"  /  "Jun" /  "Jul"  /  "Aug"
  12.             /  "Sep"  /  "Oct" /  "Nov"  /  "Dec"
  13.  
  14. time        =  hour zone                    ; ANSI and Military
  15.  
  16. hour        =  2DIGIT ":" 2DIGIT [":" 2DIGIT]
  17.                                             ; 00:00:00 - 23:59:59
  18.  
  19. zone        =  "UT"  / "GMT"                ; Universal Time
  20.                                             ; North American : UT
  21.             /  "EST" / "EDT"                ;  Eastern:  - 5/ - 4
  22.             /  "CST" / "CDT"                ;  Central:  - 6/ - 5
  23.             /  "MST" / "MDT"                ;  Mountain: - 7/ - 6
  24.             /  "PST" / "PDT"                ;  Pacific:  - 8/ - 7
  25.             /  1ALPHA                       ; Military: Z = UT;
  26.                                             ;  A:-1; (J not used)
  27.                                             ;  M:-12; N:+1; Y:+12
  28.             / ( ("+" / "-") 4DIGIT )        ; Local differential
  29.                                             ;  hours+min. (HHMM)

5.2. SEMANTICS

If included, day-of-week must be the day implied by the date specification.

Time zone may be indicated in several ways. "UT" is Universal Time (formerly called "Greenwich Mean Time"); "GMT" is permitted as a reference to Universal Time. The military standard uses a single character for each zone. "Z" is Universal Time. "A" indicates one hour earlier, and "M" indicates 12 hours earlier; "N" is one hour later, and "Y" is 12 hours later. The letter "J" is not used. The other remaining two forms are taken from ANSI standard X3.51-1975. One allows explicit indication of the amount of offset from UT; the other uses common 3-character strings for indicating time zones in North America.

6. Address Specification

6.1. Syntax 

  1. address     = mailbox ; one addressee
  2.             / group ; named list group =  phrase ":" [#mailbox] ";" mailbox = addr-spec ; simple address
  3.             /  phrase route-addr ; name & addr-spec route-addr =  "<" [route] addr-spec ">" route =  1#("@" domain) ":"           ; path-relative addr-spec = local-part "@" domain ; global address local-part = word *("." word)             ; uninterpreted
  4.                                             ; case-preserved domain = sub-domain *("." sub-domain) sub-domain = domain-ref / domain-literal domain-ref = atom ; symbolic reference

6.2. SEMANTICS

A mailbox receives mail. It is a conceptual entity which does not necessarily pertain to file storage. For example, some sites may choose to print mail on their line printer and deliver the output to the addressee's desk.

A mailbox specification comprises a person, system or process name reference, a domain-dependent string, and a name-domain reference. The name reference is optional and is usually used to indicate the human name of a recipient. The name-domain reference specifies a sequence of sub-domains. The domain-dependent string is uninterpreted, except by the final sub-domain; the rest of the mail service merely transmits it as a literal string.

6.2.1. DOMAINS 

  1. A name-domain is a set of registered (mail)  names.   A  name-
  2.    domain  specification  resolves  to  a subordinate name-domain
  3.    specification  or  to  a  terminal  domain-dependent   string.
  4.    Hence,  domain  specification  is  extensible,  permitting any
  5.    number of registration levels.
  6.  
  7.    Name-domains model a global, logical, hierarchical  addressing
  8.    scheme.   The  model is logical, in that an address specifica-
  9.    tion is related to name registration and  is  not  necessarily
  10.    tied  to  transmission  path.   The  model's  hierarchy  is  a
  11.    directed graph, called an in-tree, such that there is a single
  12.    path  from  the root of the tree to any node in the hierarchy.
  13.    If more than one path actually exists, they are considered  to
  14.    be different addresses.
  15.  
  16.    The root node is common to all addresses; consequently, it  is
  17.    not  referenced.   Its  children  constitute "top-level" name-
  18.    domains.  Usually, a service has access to its own full domain
  19.    specification and to the names of all top-level name-domains.
  20.  
  21.    The "top" of the domain addressing hierarchy -- a child of the
  22.    root  --  is  indicated  by  the right-most field, in a domain
  23.    specification.  Its child is specified to the left, its  child
  24.    to the left, and so on.
  25.  
  26.    Some groups provide formal registration services;  these  con-
  27.    stitute   name-domains   that  are  independent  logically  of
  28.    specific machines.  In addition, networks and machines  impli-
  29.    citly  compose name-domains, since their membership usually is
  30.    registered in name tables.
  31.  
  32.    In the case of formal registration, an organization implements
  33.    a  (distributed)  data base which provides an address-to-route
  34.    mapping service for addresses of the form:
  35.  
  36.                     person@registry.organization
  37.  
  38.    Note that "organization" is a logical  entity,  separate  from
  39.    any particular communication network.
  40.  
  41.    A mechanism for accessing "organization" is universally avail-
  42.    able.   That mechanism, in turn, seeks an instantiation of the
  43.    registry; its location is not indicated in the address specif-
  44.    ication.   It  is assumed that the system which operates under
  45.    the name "organization" knows how to find a subordinate regis-
  46.    try.  The registry will then use the "person" string to deter-
  47.    mine where to send the mail specification.
  48.  
  49.    The latter,  network-oriented  case  permits  simple,  direct,
  50.    attachment-related address specification, such as:
  51.  
  52.                          user@host.network
  53.  
  54.    Once the network is accessed, it is expected  that  a  message
  55.    will  go  directly  to the host and that the host will resolve
  56.    the user name, placing the message in the user's mailbox.

6.2.2. ABBREVIATED DOMAIN SPECIFICATION 

  1. Since any number of  levels  is  possible  within  the  domain
  2.    hierarchy,  specification  of  a  fully  qualified address can
  3.    become inconvenient.  This standard permits abbreviated domain
  4.    specification, in a special case:
  5.  
  6.        For the address of  the  sender,  call  the  left-most
  7.        sub-domain  Level  N.   In a header address, if all of
  8.        the sub-domains above (i.e., to the right of) Level  N
  9.        are  the same as those of the sender, then they do not
  10.        have to appear in the specification.   Otherwise,  the
  11.        address must be fully qualified.
  12.  
  13.        This feature is subject  to  approval  by  local  sub-
  14.        domains.   Individual  sub-domains  may  require their
  15.        member systems, which originate mail, to provide  full
  16.        domain  specification only.  When permitted, abbrevia-
  17.        tions may be present  only  while  the  message  stays
  18.        within the sub-domain of the sender.
  19.  
  20.        Use of this mechanism requires the sender's sub-domain
  21.        to reserve the names of all top-level domains, so that
  22.        full specifications can be distinguished from abbrevi-
  23.        ated specifications.
  25.    For example, if a sender's address is:
  26.  
  27.             sender@registry-A.registry-1.organization-X
  28.  
  29.    and one recipient's address is:
  31.            recipient@registry-B.registry-1.organization-X
  33.    and another's is:
  34.  
  35.            recipient@registry-C.registry-2.organization-X
  36.  
  37.    then ".registry-1.organization-X" need not be specified in the
  38.    the  message,  but  "registry-C.registry-2"  DOES  have  to be
  39.    specified.  That is, the first two addresses may  be  abbrevi-
  40.    ated, but the third address must be fully specified.
  41.  
  42.    When a message crosses a domain boundary, all  addresses  must
  43.    be  specified  in  the  full format, ending with the top-level
  44.    name-domain in the right-most field.  It is the responsibility
  45.    of  mail  forwarding services to ensure that addresses conform
  46.  
  47.  
  48.  
  49.    with this requirement.  In the case of abbreviated  addresses,
  50.    the  relaying  service must make the necessary expansions.  It
  51.    should be noted that it often is difficult for such a  service
  52.    to locate all occurrences of address abbreviations.  For exam-
  53.    ple, it will not be possible to find such abbreviations within
  54.    the  body  of  the  message.   The "Return-Path" field can aid
  55.    recipients in recovering from these errors.
  56.  
  57.    Note:  When passing any portion of an addr-spec onto a process
  58.           which  does  not interpret data according to this stan-
  59.           dard (e.g., mail protocol servers).  There must  be  NO
  60.           LWSP-chars  preceding  or  following the at-sign or any
  61.           delimiting period ("."), such as  shown  in  the  above
  62.           examples,   and   only  ONE  SPACE  between  contiguous
  63.           <word>s.

6.2.3. DOMAIN TERMS 

  1. A domain-ref must be THE official name of a registry, network,
  2.    or  host.   It  is  a  symbolic  reference, within a name sub-
  3.    domain.  At times, it is necessary to bypass standard  mechan-
  4.    isms  for  resolving  such  references,  using  more primitive
  5.    information, such as a network host address  rather  than  its
  6.    associated host name.
  7.  
  8.    To permit such references, this standard provides the  domain-
  9.    literal  construct.   Its contents must conform with the needs
  10.    of the sub-domain in which it is interpreted.
  11.  
  12.    Domain-literals which refer to domains within the ARPA  Inter-
  13.    net  specify  32-bit  Internet addresses, in four 8-bit fields
  14.    noted in decimal, as described in Request for  Comments  #820,
  15.    "Assigned Numbers."  For example:
  16.  
  17.                             [10.0.3.19]
  18.  
  19.    Note:  THE USE OF DOMAIN-LITERALS IS STRONGLY DISCOURAGED.  It
  20.           is  permitted  only  as  a means of bypassing temporary
  21.           system limitations, such as name tables which  are  not
  22.           complete.
  23.  
  24.    The names of "top-level" domains, and  the  names  of  domains
  25.    under  in  the  ARPA Internet, are registered with the Network
  26.    Information Center, SRI International, Menlo Park, California.

6.2.4. DOMAIN-DEPENDENT LOCAL STRING 

  1. The local-part of an  addr-spec  in  a  mailbox  specification
  2.    (i.e.,  the  host's  name for the mailbox) is understood to be
  3.  
  4.  
  5.  
  6.    whatever the receiving mail protocol server allows.  For exam-
  7.    ple,  some systems do not understand mailbox references of the
  8.    form "P. D. Q. Bach", but others do.
  9.  
  10.    This specification treats periods (".") as lexical separators.
  11.    Hence,  their  presence  in  local-parts which are not quoted-
  12.    strings, is detected.   However,  such  occurrences  carry  NO
  13.    semantics.  That is, if a local-part has periods within it, an
  14.    address parser will divide the local-part into several tokens,
  15.    but  the  sequence  of  tokens will be treated as one uninter-
  16.    preted unit.  The sequence  will  be  re-assembled,  when  the
  17.    address is passed outside of the system such as to a mail pro-
  18.    tocol service.
  19.  
  20.    For example, the address:
  21.  
  22.                       First.Last@Registry.Org
  23.  
  24.    is legal and does not require the local-part to be  surrounded
  25.    with  quotation-marks.   (However,  "First  Last" DOES require
  26.    quoting.)  The local-part of the address, when passed  outside
  27.    of  the  mail  system,  within  the  Registry.Org  domain,  is
  28.    "First.Last", again without quotation marks.

6.2.5. BALANCING LOCAL-PART AND DOMAIN 

  1. In some cases, the boundary between local-part and domain  can
  2.    be  flexible.  The local-part may be a simple string, which is
  3.    used for the final determination of the  recipient's  mailbox.
  4.    All  other  levels  of  reference  are, therefore, part of the
  5.    domain.
  6.  
  7.    For some systems, in the case of abbreviated reference to  the
  8.    local  and  subordinate  sub-domains,  it  may  be possible to
  9.    specify only one reference within the domain  part  and  place
  10.    the  other,  subordinate  name-domain  references  within  the
  11.    local-part.  This would appear as:
  12.  
  13.                    mailbox.sub1.sub2@this-domain
  14.  
  15.    Such a specification would be acceptable  to  address  parsers
  16.    which  conform  to  RFC  #733,  but  do not support this newer
  17.    Internet standard.  While contrary to the intent of this stan-
  18.    dard, the form is legal.
  19.  
  20.    Also, some sub-domains have a specification syntax which  does
  21.    not conform to this standard.  For example:
  22.  
  23.                  sub-net.mailbox@sub-domain.domain
  24.  
  25.  
  26.  
  27.    uses a different parsing  sequence  for  local-part  than  for
  28.    domain.
  29.  
  30.    Note:  As a rule,  the  domain  specification  should  contain
  31.           fields  which  are  encoded  according to the syntax of
  32.           this standard and which contain  generally-standardized
  33.           information.   The local-part specification should con-
  34.           tain only that portion of the  address  which  deviates
  35.           from the form or intention of the domain field.

6.2.6. MULTIPLE MAILBOXES 

  1. An individual may have several mailboxes and wish  to  receive
  2.    mail  at  whatever  mailbox  is  convenient  for the sender to
  3.    access.  This standard does not provide a means of  specifying
  4.    "any member of" a list of mailboxes.
  5.  
  6.    A set of individuals may wish to receive mail as a single unit
  7.    (i.e.,  a  distribution  list).  The <group> construct permits
  8.    specification of such a list.  Recipient mailboxes are  speci-
  9.    fied  within  the  bracketed  part (":" - ";").  A copy of the
  10.    transmitted message is to be  sent  to  each  mailbox  listed.
  11.    This  standard  does  not  permit  recursive  specification of
  12.    groups within groups.
  13.  
  14.    While a list must be named, it is not required that  the  con-
  15.    tents  of  the  list be included.  In this case, the <address>
  16.    serves only as an indication of group distribution  and  would
  17.    appear in the form:
  18.  
  19.                                name:;
  20.  
  21.    Some mail  services  may  provide  a  group-list  distribution
  22.    facility,  accepting  a single mailbox reference, expanding it
  23.    to the full distribution list, and relaying the  mail  to  the
  24.    list's  members.   This standard provides no additional syntax
  25.    for indicating such a  service.   Using  the  <group>  address
  26.    alternative,  while listing one mailbox in it, can mean either
  27.    that the mailbox reference will be expanded to a list or  that
  28.    there is a group with one member.

6.2.7. EXPLICIT PATH SPECIFICATION 

  1. At times, a  message  originator  may  wish  to  indicate  the
  2.    transmission  path  that  a  message  should  follow.  This is
  3.    called source routing.  The normal addressing scheme, used  in
  4.    an  addr-spec,  is  carefully separated from such information;
  5.    the <route> portion of a route-addr is provided for such occa-
  6.    sions.  It specifies the sequence of hosts and/or transmission
  7.  
  8.  
  9.  
  10.    services that are  to  be  traversed.   Both  domain-refs  and
  11.    domain-literals may be used.
  12.  
  13.    Note:  The use of source routing is discouraged.   Unless  the
  14.           sender has special need of path restriction, the choice
  15.           of transmission route should be left to the mail  tran-
  16.           sport service.

6.3. RESERVED ADDRESS

It often is necessary to send mail to a site, without knowing any of its valid addresses. For example, there may be mail system dysfunctions, or a user may wish to find out a person's correct address, at that site.

This standard specifies a single, reserved mailbox address (local-part) which is to be valid at each site. Mail sent to that address is to be routed to a person responsible for the site's mail system or to a person with responsibility for general site operation. The name of the reserved local-part address is: 

Postmaster
so that "Postmaster@domain" is required to be valid.

Note: This reserved local-part must be matched without sensitivity to alphabetic case, so that "POSTMASTER", "postmaster", and even "poStmASteR" is to be accepted.

7. Bibliography 

  1. ANSI.  "USA Standard Code  for  Information  Interchange,"  X3.4.
  2.    American  National Standards Institute: New York (1968).  Also
  3.    in:  Feinler, E.  and J. Postel, eds., "ARPANET Protocol Hand-
  4.    book", NIC 7104.
  5.  
  6. ANSI.  "Representations of Universal Time, Local  Time  Differen-
  7.    tials,  and United States Time Zone References for Information
  8.    Interchange," X3.51-1975.  American National Standards  Insti-
  9.    tute:  New York (1975).
  10.  
  11. Bemer, R.W., "Time and the Computer."  In:  Interface  Age  (Feb.
  12.    1979).
  13.  
  14. Bennett, C.J.  "JNT Mail Protocol".  Joint Network Team,  Ruther-
  15.    ford and Appleton Laboratory:  Didcot, England.
  16.  
  17. Bhushan, A.K., Pogran, K.T., Tomlinson,  R.S.,  and  White,  J.E.
  18.    "Standardizing  Network  Mail  Headers,"   ARPANET Request for
  19.    Comments No. 561, Network Information Center  No.  18516;  SRI
  20.    International:  Menlo Park (September 1973).
  21.  
  22. Birrell, A.D., Levin, R.,  Needham,  R.M.,  and  Schroeder,  M.D.
  23.    "Grapevine:  An Exercise in Distributed Computing," Communica-
  24.    tions of the ACM 25, 4 (April 1982), 260-274.
  25.  
  26. Crocker,  D.H.,  Vittal,  J.J.,  Pogran,  K.T.,  Henderson,  D.A.
  27.    "Standard  for  the  Format  of  ARPA  Network  Text Message,"
  28.    ARPANET Request for  Comments  No.  733,  Network  Information
  29.    Center  No.  41952.   SRI International:  Menlo Park (November
  30.    1977).
  31.  
  32. Feinler, E.J. and Postel, J.B.  ARPANET Protocol  Handbook,  Net-
  33.    work  Information  Center  No.  7104   (NTIS AD A003890).  SRI
  34.    International:  Menlo Park (April 1976).
  35.  
  36. Harary, F.   "Graph  Theory".   Addison-Wesley:   Reading,  Mass.
  37.    (1969).
  38.  
  39. Levin, R. and Schroeder, M.  "Transport  of  Electronic  Messages
  40.    through  a  Network,"   TeleInformatics  79, pp. 29-33.  North
  41.    Holland (1979).  Also  as  Xerox  Palo  Alto  Research  Center
  42.    Technical Report CSL-79-4.
  43.  
  44. Myer, T.H. and Henderson, D.A.  "Message Transmission  Protocol,"
  45.    ARPANET  Request  for  Comments,  No. 680, Network Information
  46.    Center No. 32116.  SRI International:  Menlo Park (1975).
  47.  
  48. NBS.  "Specification of Message Format for Computer Based Message
  49.    Systems, Recommended Federal Information Processing Standard."
  50.    National  Bureau   of   Standards:    Gaithersburg,   Maryland
  51.    (October 1981).
  52.  
  53. NIC.  Internet Protocol Transition Workbook.  Network Information
  54.    Center,   SRI-International,  Menlo  Park,  California  (March
  55.    1982).
  56.  
  57. Oppen, D.C. and Dalal, Y.K.  "The Clearinghouse:  A Decentralized
  58.    Agent  for  Locating  Named  Objects in a Distributed Environ-
  59.    ment," OPD-T8103.  Xerox Office Products Division:  Palo Alto,
  60.    CA. (October 1981).
  61.  
  62. Postel, J.B.  "Assigned Numbers,"  ARPANET Request for  Comments,
  63.    No. 820.  SRI International:  Menlo Park (August 1982).
  64.  
  65. Postel, J.B.  "Simple Mail Transfer  Protocol,"  ARPANET  Request
  66.    for Comments, No. 821.  SRI International:  Menlo Park (August
  67.    1982).
  68.  
  69. Shoch, J.F.  "Internetwork naming, addressing  and  routing,"  in
  70.    Proc. 17th IEEE Computer Society International Conference, pp.
  71.    72-79, Sept. 1978, IEEE Cat. No. 78 CH 1388-8C.
  72.  
  73. Su, Z. and Postel, J.  "The Domain Naming Convention for Internet
  74.    User  Applications,"  ARPANET  Request  for Comments, No. 819.
  75.    SRI International:  Menlo Park (August 1982).

APPENDIX A. EXAMPLES

A.1. ADDRESSES

A.1.1. Alfred Neuman <Neuman@BBN-TENEXA>

A.1.2. Neuman@BBN-TENEXA 

  1. These two "Alfred Neuman" examples have identical  seman-
  2.    tics, as far as the operation of the local host's mail sending
  3.    (distribution) program (also sometimes  called  its  "mailer")
  4.    and  the remote host's mail protocol server are concerned.  In
  5.    the first example, the  "Alfred  Neuman"  is  ignored  by  the
  6.    mailer,  as "Neuman@BBN-TENEXA" completely specifies the reci-
  7.    pient.  The second example contains  no  superfluous  informa-
  8.    tion,  and,  again,  "Neuman@BBN-TENEXA" is the intended reci-
  9.    pient.
  10.  
  11.    Note:  When the message crosses name-domain  boundaries,  then
  12.           these specifications must be changed, so as to indicate
  13.           the remainder of the hierarchy, starting with  the  top
  14.           level.

A.1.3. "George, Ted" <Shared@Group.Arpanet> 

  1. This form might be used to indicate that a single mailbox
  2.    is  shared  by several users.  The quoted string is ignored by
  3.    the originating host's mailer, because  "Shared@Group.Arpanet"
  4.    completely specifies the destination mailbox.

A.1.4. Wilt . (the Stilt) Chamberlain@NBA.US 

  1. The "(the  Stilt)" is a comment, which is NOT included in
  2.    the  destination  mailbox  address  handed  to the originating
  3.    system's mailer.  The local-part of the address is the  string
  4.    "Wilt.Chamberlain", with NO space between the first and second
  5.    words.

A.1.5. Address Lists 

  1. Gourmets:  Pompous Person <WhoZiWhatZit@Cordon-Bleu>,
  2.            Childs@WGBH.Boston, Galloping Gourmet@
  3.            ANT.Down-Under (Australian National Television),
  4.            Cheapie@Discount-Liquors;,
  5.   Cruisers:  Port@Portugal, Jones@SEA;,
  6.     Another@Somewhere.SomeOrg
  7.  
  8.  
  9.  
  10.    This group list example points out the use of comments and the
  11.    mixing of addresses and groups.

A.2. ORIGINATOR ITEMS

A.2.1. Author-sent 

  1. George Jones logs into his host  as  "Jones".   He  sends
  2.    mail himself.
  3.  
  4.        From:  Jones@Group.Org
  5.  
  6.    or
  7.  
  8.        From:  George Jones <Jones@Group.Org>

A.2.2. Secretary-sent 

  1. George Jones logs in as Jones on his  host.   His  secre-
  2.    tary,  who logs in as Secy sends mail for him.  Replies to the
  3.    mail should go to George.
  4.  
  5.        From:    George Jones <Jones@Group>
  6.        Sender:  Secy@Other-Group

A.2.3. Secretary-sent, for user of shared directory 

  1. George Jones' secretary sends mail  for  George.  Replies
  2.    should go to George.
  3.  
  4.        From:     George Jones<Shared@Group.Org>
  5.        Sender:   Secy@Other-Group
  6.  
  7.    Note that there need not be a space between  "Jones"  and  the
  8.    "<",  but  adding a space enhances readability (as is the case
  9.    in other examples.

A.2.4. Committee activity, with one author 

  1. George is a member of a committee.  He wishes to have any
  2.    replies to his message go to all committee members.
  3.  
  4.        From:     George Jones <Jones@Host.Net>
  5.        Sender:   Jones@Host
  6.        Reply-To: The Committee: Jones@Host.Net,
  7.                                 Smith@Other.Org,
  8.                                 Doe@Somewhere-Else;
  9.  
  10.    Note  that  if  George  had  not  included  himself   in   the
  11.  
  12.  
  13.  
  14.    enumeration  of  The  Committee,  he  would not have gotten an
  15.    implicit reply; the presence of the  "Reply-to"  field  SUPER-
  16.    SEDES the sending of a reply to the person named in the "From"
  17.    field.

A.2.5. Secretary acting as full agent of author 

  1. George Jones asks his secretary  (Secy@Host)  to  send  a
  2.    message for him in his capacity as Group.  He wants his secre-
  3.    tary to handle all replies.
  4.  
  5.        From:     George Jones <Group@Host>
  6.        Sender:   Secy@Host
  7.        Reply-To: Secy@Host

A.2.6. Agent for user without online mailbox 

  1. A friend  of  George's,  Sarah,  is  visiting.   George's
  2.    secretary  sends  some  mail to a friend of Sarah in computer-
  3.    land.  Replies should go to George, whose mailbox is Jones  at
  4.    Registry.
  5.  
  6.        From:     Sarah Friendly <Secy@Registry>
  7.        Sender:   Secy-Name <Secy@Registry>
  8.        Reply-To: Jones@Registry.

A.2.7. Agent for member of a committee 

  1. George's secretary sends out a message which was authored
  2.    jointly by all the members of a committee.  Note that the name
  3.    of the committee cannot be specified, since <group> names  are
  4.    not permitted in the From field.
  5.  
  6.        From:   Jones@Host,
  7.                Smith@Other-Host,
  8.                Doe@Somewhere-Else
  9.        Sender: Secy@SHost

A.3. COMPLETE HEADERS

A.3.1. Minimum required 

  1. Date:     26 Aug 76 1429 EDT        Date:     26 Aug 76 1429 EDT
  2. From:     Jones@Registry.Org   or   From:     Jones@Registry.Org
  3. Bcc:                                To:       Smith@Registry.Org
  4.  
  5.    Note that the "Bcc" field may be empty, while the  "To"  field
  6.    is required to have at least one address.

A.3.2. Using some of the additional fields 

  1. Date:     26 Aug 76 1430 EDT
  2. From:     George Jones<Group@Host>
  3. Sender:   Secy@SHOST
  4. To:       "Al Neuman"@Mad-Host,
  5.           Sam.Irving@Other-Host
  6. Message-ID:  <some.string@SHOST>

A.3.3. About as complex as you're going to get 

  1. Date     :  27 Aug 76 0932 PDT
  2. From     :  Ken Davis <KDavis@This-Host.This-net>
  3. Subject  :  Re: The Syntax in the RFC
  4. Sender   :  KSecy@Other-Host
  5. Reply-To :  Sam.Irving@Reg.Organization
  6. To       :  George Jones <Group@Some-Reg.An-Org>,
  7.             Al.Neuman@MAD.Publisher
  8. cc       :  Important folk:
  9.               Tom Softwood <Balsa@Tree.Root>,
  10.               "Sam Irving"@Other-Host;,
  11.             Standard Distribution:
  12.               /main/davis/people/standard@Other-Host,
  13.               "<Jones>standard.dist.3"@Tops-20-Host>;
  14. Comment  :  Sam is away on business. He asked me to handle
  15.             his mail for him.  He'll be able to provide  a
  16.             more  accurate  explanation  when  he  returns
  17.             next week.
  18. In-Reply-To: <some.string@DBM.Group>, George's message
  19. X-Special-action:  This is a sample of user-defined field-
  20.             names.  There could also be a field-name
  21.             "Special-action", but its name might later be
  22.             preempted
  23. Message-ID: <4231.629.XYzi-What@Other-Host>

Appendix B. Simple Field Parsing

Some mail-reading software systems may wish to perform only minimal processing, ignoring the internal syntax of structured field-bodies and treating them the same as unstructured-field-bodies. Such software will need only to distinguish:
  • Header fields from the message body,
  • Beginnings of fields from lines which continue fields,
  • Field-names from field-contents.
The abbreviated set of syntactic rules which follows will suffice for this purpose. It describes a limited view of messages and is a subset of the syntactic rules provided in the main part of this specification. One small exception is that the contents of field-bodies consist only of text:

B.1. SYNTAX 

  1. message         =   *field *(CRLF *text)
  2.  
  3. field           =    field-name ":" [field-body] CRLF
  4.  
  5. field-name      =  1*<any CHAR, excluding CTLs, SPACE, and ":">
  6.  
  7. field-body      =   *text [CRLF LWSP-char field-body]

B.2. SEMANTICS 

  1. Headers occur before the message body and are terminated  by
  2. a null line (i.e., two contiguous CRLFs).
  3.  
  4.      A line which continues a header field begins with a SPACE or
  5. HTAB  character,  while  a  line  beginning a field starts with a
  6. printable character which is not a colon.
  7.  
  8.      A field-name consists of one or  more  printable  characters
  9. (excluding  colon,  space, and control-characters).  A field-name
  10. MUST be contained on one line.  Upper and lower case are not dis-
  11. tinguished when comparing field-names.

Apppendix C. DIFFERENCES FROM RFC #733 

  1. The following summarizes the differences between this  stan-
  2. dard  and the one specified in Arpanet Request for Comments #733,
  3. "Standard for the Format of ARPA  Network  Text  Messages".   The
  4. differences  are  listed  in the order of their occurrence in the
  5. current specification.
  6.  
  7. C.1.  FIELD DEFINITIONS
  8.  
  9. C.1.1.  FIELD NAMES
  10.  
  11.    These now must be a sequence of  printable  characters.   They
  12.    may not contain any LWSP-chars.
  13.  
  14. C.2.  LEXICAL TOKENS
  15.  
  16. C.2.1.  SPECIALS
  17.  
  18.    The characters period ("."), left-square  bracket  ("["),  and
  19.    right-square  bracket ("]") have been added.  For presentation
  20.    purposes, and when passing a specification to  a  system  that
  21.    does  not conform to this standard, periods are to be contigu-
  22.    ous with their surrounding lexical tokens.   No  linear-white-
  23.    space  is  permitted  between them.  The presence of one LWSP-
  24.    char between other tokens is still directed.
  25.  
  26. C.2.2.  ATOM
  27.  
  28.    Atoms may not contain SPACE.
  29.  
  30. C.2.3.  SPECIAL TEXT
  31.  
  32.    ctext and qtext have had backslash ("\") added to the list  of
  33.    prohibited characters.
  34.  
  35. C.2.4.  DOMAINS
  36.  
  37.    The lexical tokens  <domain-literal>  and  <dtext>  have  been
  38.    added.
  39.  
  40. C.3.  MESSAGE SPECIFICATION
  41.  
  42. C.3.1.  TRACE
  43.  
  44.    The "Return-path:" and "Received:" fields have been specified.
  45.  
  46. C.3.2.  FROM
  47.  
  48.    The "From" field must contain machine-usable addresses  (addr-
  49.    spec).   Multiple  addresses may be specified, but named-lists
  50.    (groups) may not.
  51.  
  52. C.3.3.  RESENT
  53.  
  54.    The meta-construct of prefacing field names  with  the  string
  55.    "Resent-"  has been added, to indicate that a message has been
  56.    forwarded by an intermediate recipient.
  57.  
  58. C.3.4.  DESTINATION
  59.  
  60.    A message must contain at least one destination address field.
  61.    "To" and "CC" are required to contain at least one address.
  62.  
  63. C.3.5.  IN-REPLY-TO
  64.  
  65.    The field-body is no longer a comma-separated list, although a
  66.    sequence is still permitted.
  67.  
  68. C.3.6.  REFERENCE
  69.  
  70.    The field-body is no longer a comma-separated list, although a
  71.    sequence is still permitted.
  72.  
  73. C.3.7.  ENCRYPTED
  74.  
  75.    A field has been specified that permits  senders  to  indicate
  76.    that the body of a message has been encrypted.
  77.  
  78. C.3.8.  EXTENSION-FIELD
  79.  
  80.    Extension fields are prohibited from beginning with the  char-
  81.    acters "X-".

C.4. DATE AND TIME SPECIFICATION 

  1. C.4.1.  SIMPLIFICATION
  2.  
  3.    Fewer optional forms are permitted  and  the  list  of  three-
  4.    letter time zones has been shortened.

C.5. ADDRESS SPECIFICATION

C.5.1. ADDRESS 

  1. The use of quoted-string, and the ":"-atom-":" construct, have
  2.    been  removed.   An  address  now  is  either a single mailbox
  3.    reference or is a named list of addresses.  The  latter  indi-
  4.    cates a group distribution.
  5.  
  6. C.5.2.  GROUPS
  7.  
  8.    Group lists are now required to to have a name.   Group  lists
  9.    may not be nested.

C.5.3. MAILBOX 

  1. A mailbox specification  may  indicate  a  person's  name,  as
  2.    before.   Such  a  named  list  no longer may specify multiple
  3.    mailboxes and may not be nested.

C.5.4. ROUTE ADDRESSING 

  1. Addresses now are taken to be absolute, global specifications,
  2.    independent  of transmission paths.  The <route> construct has
  3.    been provided, to permit explicit specification  of  transmis-
  4.    sion  path.   RFC  #733's  use  of multiple at-signs ("@") was
  5.    intended as a general syntax  for  indicating  routing  and/or
  6.    hierarchical addressing.  The current standard separates these
  7.    specifications and only one at-sign is permitted.

C.5.5. AT-SIGN

The string " at " no longer is used as an address delimiter. Only at-sign ("@") serves the function.

C.5.6. DOMAINS

Hierarchical, logical name-domains have been added.

C.6. RESERVED ADDRESS

The local-part "Postmaster" has been reserved, so that users can be guaranteed at least one valid address at a site.

Appendix D. Alphabetical Listing of Syntax Rules 

  1. address     =  mailbox                      ; one addressee
  2.             /  group                        ; named list
  3. addr-spec   =  local-part "@" domain        ; global address
  4. ALPHA       =  <any ASCII alphabetic character>
  5.                                             ; (101-132, 65.- 90.)
  6.                                             ; (141-172, 97.-122.)
  7. atom        =  1*<any CHAR except specials, SPACE and CTLs>
  8. authentic   =   "From"       ":"   mailbox  ; Single author
  9.             / ( "Sender"     ":"   mailbox  ; Actual submittor
  10.                 "From"       ":" 1#mailbox) ; Multiple authors
  11.                                             ;  or not sender
  12. CHAR        =  <any ASCII character>        ; (  0-177,  0.-127.)
  13. comment     =  "(" *(ctext / quoted-pair / comment) ")"
  14. CR          =  <ASCII CR, carriage return>  ; (     15,      13.)
  15. CRLF        =  CR LF
  16. ctext       =  <any CHAR excluding "(",     ; => may be folded
  17.                 ")", "\" & CR, & including
  18.                 linear-white-space>
  19. CTL         =  <any ASCII control           ; (  0- 37,  0.- 31.)
  20.                 character and DEL>          ; (    177,     127.)
  21. date        =  1*2DIGIT month 2DIGIT        ; day month year
  22.                                             ;  e.g. 20 Jun 82
  23. dates       =   orig-date                   ; Original
  24.               [ resent-date ]               ; Forwarded
  25. date-time   =  [ day "," ] date time        ; dd mm yy
  26.                                             ;  hh:mm:ss zzz
  27. day         =  "Mon"  / "Tue" /  "Wed"  / "Thu"
  28.             /  "Fri"  / "Sat" /  "Sun"
  29. delimiters  =  specials / linear-white-space / comment
  30. destination =  "To"          ":" 1#address  ; Primary
  31.             /  "Resent-To"   ":" 1#address
  32.             /  "cc"          ":" 1#address  ; Secondary
  33.             /  "Resent-cc"   ":" 1#address
  34.             /  "bcc"         ":"  #address  ; Blind carbon
  35.             /  "Resent-bcc"  ":"  #address
  36. DIGIT       =  <any ASCII decimal digit>    ; ( 60- 71, 48.- 57.)
  37. domain      =  sub-domain *("." sub-domain)
  38. domain-literal =  "[" *(dtext / quoted-pair) "]"
  39. domain-ref  =  atom                         ; symbolic reference
  40. dtext       =  <any CHAR excluding "[",     ; => may be folded
  41.                 "]", "\" & CR, & including
  42.                 linear-white-space>
  43. extension-field =
  44.               <Any field which is defined in a document
  45.                published as a formal extension to this
  46.                specification; none will have names beginning
  47.                with the string "X-">
  48.  
  49.  
  50.  
  51. field       =  field-name ":" [ field-body ] CRLF
  52. fields      =    dates                      ; Creation time,
  53.                  source                     ;  author id & one
  54.                1*destination                ;  address required
  55.                 *optional-field             ;  others optional
  56. field-body  =  field-body-contents
  57.                [CRLF LWSP-char field-body]
  58. field-body-contents =
  59.               <the ASCII characters making up the field-body, as
  60.                defined in the following sections, and consisting
  61.                of combinations of atom, quoted-string, and
  62.                specials tokens, or else consisting of texts>
  63. field-name  =  1*<any CHAR, excluding CTLs, SPACE, and ":">
  64. group       =  phrase ":" [#mailbox] ";"
  65. hour        =  2DIGIT ":" 2DIGIT [":" 2DIGIT]
  66.                                             ; 00:00:00 - 23:59:59
  67. HTAB        =  <ASCII HT, horizontal-tab>   ; (     11,       9.)
  68. LF          =  <ASCII LF, linefeed>         ; (     12,      10.)
  69. linear-white-space =  1*([CRLF] LWSP-char)  ; semantics = SPACE
  70.                                             ; CRLF => folding
  71. local-part  =  word *("." word)             ; uninterpreted
  72.                                             ; case-preserved
  73. LWSP-char   =  SPACE / HTAB                 ; semantics = SPACE
  74. mailbox     =  addr-spec                    ; simple address
  75.             /  phrase route-addr            ; name & addr-spec
  76. message     =  fields *( CRLF *text )       ; Everything after
  77.                                             ;  first null line
  78.                                             ;  is message body
  79. month       =  "Jan"  /  "Feb" /  "Mar"  /  "Apr"
  80.             /  "May"  /  "Jun" /  "Jul"  /  "Aug"
  81.             /  "Sep"  /  "Oct" /  "Nov"  /  "Dec"
  82. msg-id      =  "<" addr-spec ">"            ; Unique message id
  83. optional-field =
  84.             /  "Message-ID"        ":"   msg-id
  85.             /  "Resent-Message-ID" ":"   msg-id
  86.             /  "In-Reply-To"       ":"  *(phrase / msg-id)
  87.             /  "References"        ":"  *(phrase / msg-id)
  88.             /  "Keywords"          ":"  #phrase
  89.             /  "Subject"           ":"  *text
  90.             /  "Comments"          ":"  *text
  91.             /  "Encrypted"         ":" 1#2word
  92.             /  extension-field              ; To be defined
  93.             /  user-defined-field           ; May be pre-empted
  94. orig-date   =  "Date"        ":"   date-time
  95. originator  =   authentic                   ; authenticated addr
  96.               [ "Reply-To"   ":" 1#address] )
  97. phrase      =  1*word                       ; Sequence of words
  98.  
  99.  
  100.  
  101.  
  102.  
  103. qtext       =  <any CHAR excepting <">,     ; => may be folded
  104.                 "\" & CR, and including
  105.                 linear-white-space>
  106. quoted-pair =  "\" CHAR                     ; may quote any char
  107. quoted-string = <"> *(qtext/quoted-pair) <">; Regular qtext or
  108.                                             ;   quoted chars.
  109. received    =  "Received"    ":"            ; one per relay
  110.                   ["from" domain]           ; sending host
  111.                   ["by"   domain]           ; receiving host
  112.                   ["via"  atom]             ; physical path
  113.                  *("with" atom)             ; link/mail protocol
  114.                   ["id"   msg-id]           ; receiver msg id
  115.                   ["for"  addr-spec]        ; initial form
  116.                    ";"    date-time         ; time received
  118. resent      =   resent-authentic
  119.               [ "Resent-Reply-To"  ":" 1#address] )
  120. resent-authentic =
  121.             =   "Resent-From"      ":"   mailbox
  122.             / ( "Resent-Sender"    ":"   mailbox
  123.                 "Resent-From"      ":" 1#mailbox  )
  124. resent-date =  "Resent-Date" ":"   date-time
  125. return      =  "Return-path" ":" route-addr ; return address
  126. route       =  1#("@" domain) ":"           ; path-relative
  127. route-addr  =  "<" [route] addr-spec ">"
  128. source      = [  trace ]                    ; net traversals
  129.                  originator                 ; original mail
  130.               [  resent ]                   ; forwarded
  131. SPACE       =  <ASCII SP, space>            ; (     40,      32.)
  132. specials    =  "(" / ")" / "<" / ">" / "@"  ; Must be in quoted-
  133.             /  "," / ";" / ":" / "\" / <">  ;  string, to use
  134.             /  "." / "[" / "]"              ;  within a word.
  135. sub-domain  =  domain-ref / domain-literal
  136. text        =  <any CHAR, including bare    ; => atoms, specials,
  137.                 CR & bare LF, but NOT       ;  comments and
  138.                 including CRLF>             ;  quoted-strings are
  139.                                             ;  NOT recognized.
  140. time        =  hour zone                    ; ANSI and Military
  141. trace       =    return                     ; path to sender
  142.                1*received                   ; receipt tags
  143. user-defined-field =
  144.               <Any field which has not been defined
  145.                in this specification or published as an
  146.                extension to this specification; names for
  147.                such fields must be unique and may be
  148.                pre-empted by published extensions>
  149. word        =  atom / quoted-string
  150.  
  151.  
  152.  
  153.  
  154.  
  155. zone        =  "UT"  / "GMT"                ; Universal Time
  156.                                             ; North American : UT
  157.             /  "EST" / "EDT"                ;  Eastern:  - 5/ - 4
  158.             /  "CST" / "CDT"                ;  Central:  - 6/ - 5
  159.             /  "MST" / "MDT"                ;  Mountain: - 7/ - 6
  160.             /  "PST" / "PDT"                ;  Pacific:  - 8/ - 7
  161.             /  1ALPHA                       ; Military: Z = UT;
  162. <">         =  <ASCII quote mark>           ; (     42,      34.)

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