RFC #   733
NIC # 41952
Obsoletes:  RFC #561  (NIC #18516)

RFC #680 (NIC #32116)

RFC #724 (NIC #37435)

STANDARD FOR THE FORMAT OF

ARPA NETWORK TEXT MESSAGES(1)

21 November 1977

by

David H. Crocker
The Rand Corporation

John J. Vittal
Bolt Beranek and Newman Inc.

Kenneth T. Pogran
Massachusets Institute of Technology

D. Austin Henderson, Jr.(2)
Bolt Beranek and Newman Inc.

_________________________________________________________________
(1)This work was supported by the Defense Advanced Research
Projects Agency of the Department of Defense, under contract Nos.
N00014-75-C-0661, MDA903-76-C-0212, and DAHC15-73-C0181.

(2)The authors' postal addresses are: D. Crocker, The Rand
Corporation, Information Sciences Dept., 1700 Main St., Santa
Monica, California 90406; J. Vittal & D. A. Henderson, Bolt
Beranek & Newman, 50 Moulton St., Cambridge, Massachusetts 02138;
and K. Pogran, MIT Laboratory for Computer Science, 545
Technology Square, Cambridge, Massachusetts 02139. The authors'
ARPANET addresses are: DCrocker at Rand-Unix, Vittal at BBN-
TenexD, Pogran at MIT-Multics, and Henderson at BBN-TenexD.
PREFACE 

     ARPA's  Committee  on  Computer-Aided  Human   Communication
(CAHCOM) wishes to promulgate a standard for the format of ARPA
Network text message (mail) headers which will reasonably meet
the needs of the various message service subsystems on the
Network today. The authors of this document constitute the
CAHCOM subcommittee charged with the task of developing this new
standard.

Essentially, we specify a revision to ARPANET Request for

Comments (RFC) 561, "Standardizing Network Mail Headers", and RFC
680, "Message Transmission Protocol". This revision removes and
compacts portions of the previous syntax and adds several
features to network address specification. In particular, we
focus on people and not mailboxes as recipients and allow
reference to stored address lists. We expect this syntax to
provide sufficient capabilities to meet most users' immediate
needs and, therefore, give developers enough breathing room to
produce a new mail transmission protocol "properly". We believe
that there is enough of a consensus in the Network community in
favor of such a standard syntax to make possible its adoption at
this time. An earlier draft of this specification was published
as RFC #724, "Proposed Official Standard for the Format of ARPA
Network Messages" and contained extensive discussion of the
background and issues in ARPANET mail standards.

This specification was developed 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 this discussion and we would like to acknowledge
their considerable efforts. The syntax of the standard was
originally specified in the Backus-Naur Form (BNF) meta-language.
Ken L. Harrenstien, of SRI International, was responsible for
re-coding the BNF into an augmented BNF which compacts the
specification and allows increased comprehensibility.

CONTENTS

PREFACE

Section
I. INTRODUCTION

II. FRAMEWORK

III. SYNTAX
A. Notational Conventions
B. Lexical Analysis of Messages
C. General Syntax of Messages
D. Syntax of General Addressee Items
E. Supporting Constructs

IV. SEMANTICS
A. Address Fields
B. Reference Specification Fields
C. Other Fields and Syntactic Items
D. Dates and Times

V. EXAMPLES
A. Addresses
B. Address Lists
C. Originator Items
D. Complete Headers

Appendix
A. ALPHABETICAL LISTING OF SYNTAX RULES
B. SIMPLE PARSING

BIBLIOGRAPHY

I. Introduction

I. INTRODUCTION

This standard specifies a syntax for text messages which are

passed between computer users within the framework of "electronic
mail". The standard supersedes the informal standards specified
in ARPANET Request for Comments numbers 561, "Standardizing
Network Mail Headers", and 680, "Message Transmission Protocol".
In this document, a general framework is first described; the
formal syntax is then specified, followed by a discussion of the
semantics. Finally, a number of examples are given.

This specification is intended strictly as a definition of

what is to be passed between hosts on the ARPANET. It is NOT
intended to dictate either features which systems on the Network
are expected to support, or user interfaces to message creating
or reading programs.

A distinction should be made between what the specification

REQUIRES and what it ALLOWS. Messages can be made complex and
rich with formally-structured components of information or can be
kept small and simple, with a minimum of such information. Also,
the standard simplifies the interpretation of differing visual
formats in messages. These simplifications facilitate the formal
specification and indicate what the OFFICIAL semantics are for
messages. Only the visual aspect of a message is affected and
not the interpretation of information within it. Implementors
may choose to retain such visual distinctions.

II. Framework

II. FRAMEWORK

Since there are many message systems which exist outside the

ARPANET environment, as well as those within it, it may be useful
to consider the general framework, and resulting capabilities and
limitations, provided by this standard.

Messages are expected to consist of lines of text. No

special provisions are made, at this time, for encoding drawings,
facsimile, speech, or structured text.

No significant consideration has been given to questions of

data compression or transmission/storage efficiency. The
standard, in fact, tends to be very free with the number of bits
consumed. For example, field names are specified as free text,
rather than special terse codes.

A general "memo" framework is used. That is, a message

consists of some information, in a rigid format, followed by the
main part of the message, which is text and whose format is not
specified in this document. The syntax of several fields of the
rigidly-formated ("header") section is defined in this
specification; some of the header fields must be included in all
messages. The syntax which distinguishes between headers is
specified separately from the internal syntax for particular
headers. This separation is intended to allow extremely simple
parsers to operate on the overall structure of messages, without
concern for the detailed structure of individual headers.
Appendix B is provided to facilitate construction of these simple
parsers. In addition to the fields specified in this document,
it is expected that other fields will gain common use. User-
defined header fields allow systems to extend their functionality
while maintaining a uniform framework. The approach is similar
to that of the TELNET protocol, in that a basic standard is
defined which includes a mechanism for (optionally) extending
itself. As necessary, the authors of this document will regulate
the publishing of specifications for these "extension-fields",
through the same mechanisms used to publish this document.

Such a framework severely constrains document tone and

appearance and is primarily useful for most intra-organization
communications and relatively structured inter-organization
communication. A more robust environment might allow for multi-
font, multi-color, multi-dimension encoding of information. A
less robust environment, as is present in most single-machine
message systems, would more severely constrain the ability to add
fields and the decision to include specific fields. In contrast
to paper-based communication, it is interesting to note that the
II. Framework

RECEIVER of a message can exercise an extraordinary amount of
control over the message's appearance. The amount of actual
control available to message receivers is contingent upon the
capabilities of their individual message systems.

III. Syntax

III. SYNTAX

This syntax is given in five parts. The first part

describes the notation used in the specification. The second
part describes the base-level lexical analyzers which feed the
higher-level parser described in the succeeding sections. The
third part gives a general syntax for messages and standard
header fields; and the fourth part specifies the syntax of
addresses. A final part specifies some general syntax which
supports the other sections.

A. NOTATIONAL CONVENTIONS

These specifications are made in an augmented Backus-Naur Form
(BNF). Differences from standard BNF involve the naming of
rules, the indication of repetition and of "local" alternatives.

1. Rule naming

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

2. Parentheses: Local alternatives

Elements enclosed in parentheses are treated as a single element.
Thus, "(elem (foo / bar) elem)" allows "(elem foo elem)" and
"(elem bar elem)".

3. * construct: Repetition

The character "*" preceding an element indicates repetition. The
full form is:

          <l>*<m>element

indicating at least <l> and at most <m> occurrences of element.
Default values are 0 and infinity so that "*(element)" allows any
number, including zero; "1*element" requires at least one; and
"1*2element" allows one or two.
III. Syntax
A. Notational Conventions

4. <number>element

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

5. # construct: Lists

A construct "#" is defined, similar to "*", as follows:

                  <l>#<m>element

indicating at least <l> and at most <m> elements, each separated
by one or more commas (","). This makes the usual form of lists
very easy; a rule such as '(element *("," element))' can be shown
as "1#element". Wherever this construct is used, null elements
are allowed, but do not contribute to the count of elements
present. That is, "(element),,(element)" is permitted, but
counts as only two elements. Therefore, where at least one
element is required, at least one non-null element must be
present.

6. [optional]

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

7. ; Comments

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

B. LEXICAL ANALYSIS OF MESSAGES

1. General Description

A message consists of headers and, optionally, a body (i.e. a
series of text lines). The text part is just 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).

III. Syntax
B. Lexical Analysis

a. Folding and unfolding of headers

Each header item can be viewed as a single, logical line of ASCII characters. For convenience, the field-body portion of this conceptual entity can be split into a multiple-line representation (i.e., "folded"). The general rule is that wherever there can be linear-white-space (NOT simply LWSP- chars), a CRLF immediately followed by AT LEAST one LWSP-char can instead be inserted. (However, a header's name and the following colon (":"), which occur at the beginning of the 

    header item, may NOT be folded onto multiple  lines.)   Thus,
    the single line

To: "Joe Dokes & J. Harvey" <ddd at Host>, JJV at BBN

can be represented as

To: "Joe Dokes & J. Harvey" <ddd at Host>,
JJV at BBN

and

To: "Joe Dokes & J. Harvey" 

                        <ddd at Host>,
        JJV at BBN

and

To: "Joe Dokes
& J. Harvey" <ddd at Host>, JJV at BBN 

    The  process  of  moving  from  this   folded   multiple-line
    representation   of   a  header  field  to  its  single  line
    representation will  be  called  "unfolding".   Unfolding  is
    accomplished  by  regarding  CRLF  immediately  followed by a
    LWSP-char as equivalent  to  the  LWSP-char.

b. Structure of header fields

Once header fields have been unfolded, they may be viewed as being composed of a field-name followed by a colon (":"), followed by a field-body. The field-name must be composed of printable ASCII characters (i.e., characters which have values between 33. and 126., decimal, except colon) and LWSP-chars. The field-body may be composed of any ASCII characters (other than an unquoted CRLF, which has been removed by unfolding).

Certain field-bodies of header fields may be interpreted according to an internal syntax which some systems may wish to parse. These fields will be referred to as "structured" 

    fields.    Examples   include  fields  containing  dates  and
III. Syntax
B. Lexical Analysis

addresses. Other fields, such as "Subject" and "Comments", are regarded simply as strings of text.

NOTE: Field-names, unstructured field bodies and structured field bodies each are scanned by their own, INDEPENDENT "lexical" analyzer.

c. Field-names

To aid in the creation and reading of field-names, the free insertion of LWSP-chars is allowed in reasonable places.

Rather than obscuring the syntax specification for field-name with the explicit syntax for these LWSP-chars, the existence of a "lexical" analyzer is assumed. The analyzer interprets the text which comprises the field-name as a sequence of field-name atoms (fnatoms) separated by LWSP-chars

Note that ONLY LWSP-chars may occur between the fnatoms of a field-name and that CRLFs may NOT. In addition, comments are NOT lexically recognized, as such, but parenthesized strings are legal as part of field-names. These constraints are different from what is permissible within structured field bodies. In particular, this means that header field-names must wholly occur on the FIRST line of a folded header item and may NOT be split across two or more lines.

d. Unstructured field bodies

For some fields, such as "Subject" and "Comments", no structuring is assumed; and they are treated simply as texts, like those 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.

e. 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 in reasonable places. 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 field bodies which are simply unstructured strings of text, as described above. It provides an interpretation of the unfolded text comprising the body of the field as a sequence of lexical symbols. These symbols are: 

            -  individual special characters
            -  quoted-strings
III. Syntax
B. Lexical Analysis 

            -  comments
            -  atoms

The first three of these symbols are self-delimiting. Atoms are not; they therefore are delimited by the self-delimiting symbols and by linear-white-space. For the purposes of re- generating sequences of atoms and quoted-strings, exactly one SPACE is assumed to exist and should be used between them. (Also, in Section III.B.3.a, note the rules concerning treatment of multiple continguous LWSP-chars.)

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

            ":sysmail"@   Some-Host,
            Muhammed(I am   the greatest)Ali   at(the)WBA

is analyzed into the following lexical symbols and types: 

            ":sysmail"              quoted string
            @                       special
            Some-Host               atom
            ,                       special
            Muhammed                atom
            (I am   the greatest)   comment
            Ali                     atom
            at                      atom
            (the)                   comment
            WBA                     atom

The cononical representations for the data in these addresses are the following strings (note that there is exactly one SPACE between words):

:sysmail at Some-Host

and

Muhammed Ali at WBA

2. Formal Definitions

The first four rules, below, indicate a meta-syntax for fields,
without regard to their particular type or internal syntax. The
remaining rules define basic syntactic structures which are used
by the rules in Sections III.C, III.D, and III.E.

field = field-name ":" [ field-body ] CRLF

field-name = fnatom *( LWSP-char [fnatom] )

III. Syntax
B. Lexical Analysis

fnatom = 1*<any CHAR, excluding CTLs, SPACE, and ":">

field-body = field-body-contents
[CRLF LWSP-char field-body]

field-body-contents = <the TELNET ASCII characters making up the
field-body, as defined in the following sections, and consisting of combinations of atom, quoted- string, and specials tokens, or else consisting of texts> 

                                            ; (  Octal, Decimal.)
CHAR        =  <any TELNET ASCII character> ; (  0-177,  0.-127.)
ALPHA       =  <any TELNET ASCII alphabetic character>
                                            ; (101-132, 65.- 90.)
                                            ; (141-172, 97.-122.)
DIGIT       =  <any TELNET ASCII digit>     ; ( 60- 71, 48.- 57.)
CTL         =  <any TELNET ASCII control    ; (  0- 37,  0.- 31.)
                character and DEL>          ; (    177,     127.)
CR          =  <TELNET ASCII carriage return>;(     15,      13.)
LF          =  <TELNET ASCII linefeed>      ; (     12,      10.)
SPACE       =  <TELNET ASCII space>         ; (     40,      32.)
HTAB        =  <TELNET ASCII horizontal-tab>; (     11,       9.)
<">         =  <TELNET ASCII quote mark>    ; (     42,      34.)
CRLF        =  CR LF

LWSP-char = SPACE / HTAB ; semantics = SPACE
linear-white-space = 1*([CRLF] LWSP-char) ; semantics = SPACE
                                            ; CRLF => folding

specials = "(" / ")" / "<" / ">" / "@" ; To use in a word,
            /  "," / ";" / ":" / "\" / <">  ;  word must be a
                                            ;  quoted-string.

delimiters = specials / comment / linear-white-space

text = <any CHAR, including bare ; => atoms, specials,
CR and/or bare LF, but NOT ; comments and 
                including CRLF>             ;  quoted-strings are
                                            ;  NOT interpreted.

atom = 1*<any CHAR except specials and CTLs>

quoted-string = <"> *(qtext/quoted-pair) <">; Any number of qtext
                                            ;   chars or any
                                            ;   quoted char.

qtext = <any CHAR excepting <"> ; => may be folded
and CR, and including
linear-white-space>

III. Syntax
B. Lexical Analysis

comment = "(" *(ctext / comment / quoted-pair) ")"
ctext = <any CHAR excluding "(", ; => may be folded
")" and CR, and including
linear-white-space>

quoted-pair = "\" CHAR

3. Clarifications

a. "White space"

Remember that in field-names and structured field bodies, MULTIPLE LINEAR WHITE SPACE TELNET ASCII CHARACTERS (namely HTABs and SPACEs) ARE TREATED AS SINGLE SPACES AND MAY FREELY SURROUND ANY SYMBOL. In all header fields, the only place in which at least one space is REQUIRED is at the beginning of continuation lines in a folded field. When passing text to processes which do not interpret text according to this standard (e.g., ARPANET FTP mail servers), then exactly one SPACE should be used in place of arbitrary linear-white-space and comment sequences.

WHEREVER A MEMBER OF THE LIST OF <DELIMITER>S IS ALLOWED, LWSP-CHARS MAY ALSO OCCUR BEFORE AND/OR AFTER IT.

Writers of mail-sending (i.e. header generating) programs should realize that there is no Network-wide definition of the effect of horizontal-tab TELNET ASCII characters on the appearance of text at another Network host; therefore, the 

    use  of  tabs  in  message  headers,  though  permitted,   is
    discouraged.

Note that during transmissions across the ARPANET using TELNET NVT connections, data must conform to TELNET NVT conventions (e.g., CR must be followed by either LF, making a CRLF, or <null>, if the CR is to stand alone).

b. Comments

Comments are detected as such only within field-bodies of structured fields. A comment is a set of TELNET ASCII characters, which is not within a quoted-string and which is enclosed in matching parentheses; parentheses nest, so that if an unquoted left parenthesis occurs in a comment string, there must also be a matching right parenthesis. When a comment is used to act as the delimiter between a sequence of two lexical symbols, such as two atoms, it is lexically equivalent with one SPACE, for the purposes of regenerating the sequence, such as when passing the sequence onto an FTP mail server.

III. Syntax
B. Lexical Analysis

In particular comments are NOT passed to the FTP server, as part of a MAIL or MLFL command, since comments are not part of the "formal" address.

If a comment is to be "folded" onto multiple lines, then the syntax for folding must be adhered to. (See items III.B.1.a, 

    above,  and  III.B.3.f,  below.)   Note  that  the   official
    semantics therefore do not "see" any unquoted CRLFs which are
    in comments, although particular parsing programs may wish to
    note  their  presence.   For  these  programs,  it  would  be
    reasonable to interpret a "CRLF LWSP-char" as  being  a  CRLF
    which  is part of the comment; i.e., the CRLF is kept and the
    LWSP-char is discarded.   Quoted  CRLFs  (i.e.,  a  backslash
    followed  by a CR followed by a LF) still must be followed by
    at least one LWSP-char.

c. Delimiting and quoting characters

The quote character (backslash) and characters which delimit syntactic units are not, generally, to be taken as data which are part of the delimited or quoted unit(s). The one exception is SPACE. In particular, the quotation-marks which define a quoted-string, the parentheses which define a comment and the backslash which quotes a following character 

    are  NOT  part  of  the  quoted-string,  comment  or   quoted
    character.   A  quotation-mark  which  is  to  be  part  of a
    quoted-string, a parenthesis which is to be part of a comment
    and  a  backslash  which is to be part of either must each be
    preceded by the quote-character backslash ("\").   Note  that
    the  syntax  allows  any  character  to  be  quoted  within a
    quoted-string or comment;  however  only  certain  characters
    MUST  be quoted to be included as data.  These characters are
    those which are not part of the alternate text  group  (i.e.,
    ctext or qtext).

A single SPACE is assumed to exist between contiguous words in a phrase, and this interpretation is independent of the actual number of LWSP-chars which the creator places between the words. To include more than one SPACE, the creator must make the LWSP-chars be part of a quoted-string.

Quotation marks which delimit a quoted string and backslashes which quote the following character should NOT accompany the quoted-string when the string is used with processes that do not interpret data according to this specification (e.g., ARPANET FTP mail servers).

III. Syntax
B. Lexical Analysis

d. Quoted-strings

    Where   permitted  (i.e.,  in  words  in  structured  fields)
    quoted-strings   are   treated   as  a  single  symbol  (i.e.
    equivalent to an atom, syntactically).  If a quoted-string is
    to  be  "folded"  onto  multiple  lines,  then the syntax for
    folding must be adhered to.  (See items III.B.1.a, above, and
    III.B.3.f,   below.)    Note   that  the  official  semantics
    therefore do not "see" any bare CRLFs which  are  in  quoted-
    strings,  although  particular  parsing  programs may wish to
    note  their  presence.   For  these  programs,  it  would  be
    reasonable  to  interpret  a "CRLF LWSP-char" as being a CRLF
    which is part of the quoted-string; i.e., the  CRLF  is  kept
    and  the  LWSP-char  is  discarded.   Quoted  CRLFs  (i.e., a
    backslash followed by a CR followed by a LF) are also subject
    to  rules  of  folding,  but  the  presence  of  the  quoting
    character (backslash) explicitly indicates that the  CRLF  is
    data to the quoted string.  Stripping off the first following
    LWSP-char is also appropriate when parsing quoted CRLFs.

e. Bracketing characters

There are three types of brackets which must be well nested:

f. Case independence of certain specials atoms

Certain atoms, which are represented in the syntax as literal alphabetic strings, can be represented in any combination of upper and lower case. These are: 

        -  field-name,
        -  "Include", "Postal" and equivalent atoms in a
           ":"<atom>":" address specification,
        -  "at", in a host-indicator,
        -  node,
        -  day-of-week,
        -  month, and
        -  zones.

When matching an atom against one of these literals, case is to be ignored. For example, the field-names "From", "FROM",

III. Syntax
B. Lexical Analysis

"from", and even "FroM" should all be treated identically. However, the case shown in this specification is suggested for message-creating processes. Note that, at the level of this specification, case IS relevant to other words and texts. Also see Section IV.A.1.f, below.

g. Folding long lines

Each header item (field of the message) may be represented on exactly one line consisting of the name of the field and its body; this is what the parser sees. For readability, it is recommended that the field-body portion of long header items be "folded" onto multiple lines of the actual header. "Long" is commonly interpreted to mean greater than 65 or 72 characters. The former length is recommended as a limit, but it is not imposed by this standard.

h. Backspace characters

Backspace TELNET ASCII characters (ASCII BS, decimal 8.) may 

    be   included   in   texts   and   quoted-strings  to  effect
    overstriking; however, any use of backspaces which effects an
    overstrike  to  the  left  of  the  beginning  of the text or
    quoted-string is prohibited.

C. GENERAL SYNTAX OF MESSAGES:

NOTE: Due to an artifact of the notational conventions, the syntax indicates that, when present, "Date", "From", "Sender", and "Reply-To" fields must be in a particular order. These header items must be unique (occur exactly once). However header fields, in fact, are NOT required to occur in any particular order, except that the message body must occur AFTER the headers. For readability and ease of parsing by simple systems, it is recommended that headers be sent in the order "Date", "From", "Subject", "Sender", "To", "cc", 

           etc.    This   specification   permits   multiple
           occurrences of  most  optional-fields.   However,
           their  interpretation  is not specified here, and
           their use is strongly discouraged.

The following syntax for the bodies of various fields should be
thought of as describing each field body as a single long string
(or line). The section on Lexical Analysis (section II.B)
indicates how such long strings can be represented on more than
one line in the actual transmitted message.

III. Syntax
C. Messages

message = fields *( CRLF *text ) ; Everything after
                                            ;  first null line
                                            ;  is message body

fields = date-field ; Creation time-stamp
               originator-fields            ;  & author id are
               *optional-field              ;  required: others
                                            ;  are all optional

originator-fields =
               (  "From"     ":" mailbox    ; Single author
                 ["Reply-To" ":" #address] )
            /  (  "From"     ":" 1#address  ; Multiple authors &
                  "Sender"   ":" mailbox    ;  may have non-mach-
                 ["Reply-To" ":" #address] );  ine addresses

date-field = "Date" ":" date-time

optional-field =
               "To"         ":" #address
            /  "cc"         ":" #address
            /  "bcc"        ":" #address    ; Blind carbon
            /  "Subject"    ":" *text
            /  "Comments"   ":" *text
            /  "Message-ID" ":" mach-id     ; Only one allowed
            /  "In-Reply-To"":" #(phrase / mach-id)
            /  "References" ":" #(phrase / mach-id)
            /  "Keywords"   ":" #phrase
            /  extension-field              ; To be defined in
                                            ;  supplemental
                                            ;  specifications
            /  user-defined-field           ; Must have unique
                                            ;  field-name & may
                                            ;  be pre-empted

extension-field = <Any field which is defined in a document
published as a formal extension to this
specification>

user-defined-field = <Any field which has not been defined in
this specification or published as an extension to this specification; names for such fields must be unique and may be preempted by published
extensions>

III. Syntax
D. Addressee Items

D. SYNTAX OF GENERAL ADDRESSEE ITEMS

address = host-phrase ; Machine mailbox
            / ( [phrase] "<" #address ">")  ; Individual / List
            / ( [phrase] ":" #address ";")  ; Group
            /  quoted-string                ; Arbitrary text
            / (":" ( "Include"              ; File, w/ addr list
                   / "Postal"               ; (U.S.) Postal addr
                   /  atom )                ; Extended data type
               ":" address)

mailbox = host-phrase / (phrase mach-id)

mach-id = "<" host-phrase ">" ; Contents must never
                                            ;  be modified!

E. SUPPORTING CONSTRUCTS

host-phrase = phrase host-indicator ; Basic address

host-indicator = 1*( ("at" / "@") node ) ; Right-most node is
                                            ;  at top of network
                                            ;  hierarchy; left-
                                            ;  most must be host

node = word / 1*DIGIT ; Official host or
                                            ;  network name or
                                            ;  decimal address

date-time = [ day-of-week "," ] date time

day-of-week = "Monday" / "Mon" / "Tuesday" / "Tue"
            /  "Wednesday" / "Wed"  / "Thursday"  / "Thu"
            /  "Friday"    / "Fri"  / "Saturday"  / "Sat"
            /  "Sunday"    / "Sun"

date = 1*2DIGIT ["-"] month ; day month year
               ["-"] (2DIGIT /4DIGIT)       ;  e.g. 20 Aug [19]77

month = "January" / "Jan" / "February" / "Feb"
            /  "March"     / "Mar"  / "April"     / "Apr"
            /  "May"                / "June"      / "Jun"
            /  "July"      / "Jul"  / "August"    / "Aug"
            /  "September" / "Sep"  / "October"   / "Oct"
            /  "November"  / "Nov"  / "December"  / "Dec"

III. Syntax
E. Supporting Constructs

time = hour zone ; ANSI and Military
                                            ;  (seconds optional)

hour = 2DIGIT [":"] 2DIGIT [ [":"] 2DIGIT ]
                                            ; 0000[00] - 2359[59]

zone = ( ["-"] ( "GMT" ; Relative to GMT:
                                            ; North American
                 /  "NST" /                 ;  Newfoundland:-3:30
                 /  "AST" / "ADT"           ;  Atlantic: - 4/ - 3
                 /  "EST" / "EDT"           ;  Eastern:  - 5/ - 4
                 /  "CST" / "CDT"           ;  Central:  - 6/ - 5
                 /  "MST" / "MDT"           ;  Mountain: - 7/ - 6
                 /  "PST" / "PDT"           ;  Pacific:  - 8/ - 7
                 /  "YST" / "YDT"           ;  Yukon:    - 9/ - 8
                 /  "HST" / "HDT"           ;  Haw/Ala   -10/ - 9
                 /  "BST" / "BDT"           ;  Bering:   -11/ -10
                    1ALPHA       ))         ; Military: Z = GMT;
                                            ;  A:-1; (J not used)
                                            ;  M:-12; N:+1; Y:+12
            / ( ("+" / "-") 4DIGIT )        ; Local differential
                                            ;  hours/min. (HHMM)

phrase = 1*word ; Sequence of words.
                                            ;  Separation seman-
                                            ;  tically = SPACE

word = atom / quoted-string

IV. Semantics
A. Address Fields

IV. SEMANTICS

A. ADDRESS FIELDS

1. General

a. The phrase part of a host-phrase in an address specification
(i.e., the host's name for the mailbox) is understood to be whatever the receiving FTP Server allows (for example, TENEX systems do not now understand addresses of the form "P. D. Q. Bach", but another system might).

Note that a mailbox 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.

An individual may have several mailboxes and a group of individuals may wish to receive mail as a single unit (i.e., a distribution list). The second and third alternatives of an address list (#address) allow naming a collection of 

    subordinate  addresses  list(s).   Recipient  mailboxes   are
    specified  within the bracketed part ("<" - ">" or ":" - ";")
    of such named lists.  The use of angle-brackets ("<", ">") is
    intended for the cases of individuals with multiple mailboxes
    and of special mailbox lists; it is not expected to be nested
    more  than  one level, although the specification allows such
    nesting.  The use of colon/semi-colon (":", ";") is  intended
    for  the  case  of  groups.   Groups  can be expected to nest
    (i.e., to  contain  subgroups).   For  both  individuals  and
    groups,  a  copy  of the transmitted message is to be sent to
    EACH mailbox  listed.   For  the  case  of  a  special  list,
    treatment of addresses is defined in the relevant subsections
    of this section.

b. The inclusion of bare quoted-strings as addresses (i.e., the
fourth address-form alternative) is allowed as a syntactic convenience, but no semantics are defined for their use. However, it is reasonable, when replicating an address list, to replicate ALL of its members, including quoted-strings.

c. ":Include:" specifications are used to refer to one or more
locations containing stored address lists (#address). If more than one location is referenced, the address part of the Include phrase must be a list (#address) surrounded by angle-brackets, as per the "Individual / List" alternative of 
    <address>.   Constituent  addresses  must  resolve to a host-
IV. Semantics
A. Address Fields

phrase; only they have any meaning within this construct. The phrase part of indicated host-phrases should contain text which the referenced host can resolve to a file. This standard is not a protocol and so does not prescribe HOW data is to be retrieved from the file. However, the following requirements are made:

It is intended that this mechanism allow programs to retrieve such lists automatically.

The interpretation of such a file reference follows. This is not intended to imply any particular implementation scheme, but is presented to aid in understanding the notion of including file contents in address lists:

d. ":Postal:" specifications are used to indicate (U.S.) postal
addresses, but can be treated the same as quoted-string addresses. To reference a list of postal addresses, the list must conform to the "Individual / List" alternative of 
    <address>.  The ":Include:" alternative also is valid.

e. The "':' atom ':'" syntax is intended as a general mechanism
for indicating specially data-typed addresses. As with extension-fields, the authors of this document will regulate
IV. Semantics
A. Address Fields

the publishing of specifications for these extended data- types. In the absence of defined semantics, any occurrence of an address in this form may be treated as a quoted-string address.

f. A node name must be THE official name of a network or a host,
or else a decimal number indicating the Network address for that network or host, at the time the message is created. The USE OF NUMBERS IS STRONGLY DISCOURAGED and is permitted only due to the occasional necessity of bypassing local name tables. For the ARPANET, official names are maintained by the Network Information Center at SRI International, Menlo Park, California.

Whenever a message might be transmitted or migrate to a host on another network, full hierarchical addresses must be specified. These are indicated as a series of words, separated by at-sign or "at" indications. The communication environment is assumed to consist of a collection of networks organized as independent "trees" except for connections between the root nodes. That is, only the roots can act as gateways between these independent networks. While other actual connections may exist, it is believed that presuming this type of organization will provide a reliable method for describing VALID, if not EFFICIENT, paths between hosts. A typical full mailbox specification might therefore look like:

Friendly User @ hosta @ local-net1 @ major-netq

In the simplest case, a mail-sending host should transmit the message to the node which is mentioned last (farthest to the right), strip off that node reference from the specification, and then pass the remaining host-phrase to the recipient host (in the ARPANET, its FTP server) for it to process. This treats the remaining portion of the host-indicator merely as the terminating part of the phrase.

NOTE: When passing any portion of a host-indicator onto a process which does not interpret data according to this standard (e.g., ARPANET FTP servers), "@" must be used and not "at" and it must not be preceded or followed by any LWSP-chars. Using the above example, the following string would be passed to the major-netq gateway:

Friendly User@hosta@local-net1

When the sending host has more knowledge of the network environment, then it should send the message along a more efficient path, making appropriate changes to the form of the host-phrase which it gives to the recipient host.

IV. Semantics
A. Address Fields

To use the above specification as an example: If a sending hostb also were part of local-net1, then it could send the message directly to hosta and would give only the phrase "Friendly User" to hosta's mail-receiving program. If hostb were part of local-net2, along with hostc, and happened to know that hosta and hostc were part of another local-net, then hostb could send the message to hostc to the address "Friendly User@hosta".

The phrase in a host-phrase is intended to be meaningful only to the indicated receiving host. To all other hosts, the phrase is to be treated as an uninterpreted string. No case transformations should be (automatically) performed on the phrase. The phrase is passed to the local host's mail sending program; it is the responsibility of the destination host's mail receiving (distribution) program to perform case mapping on this phrase, if required, to deliver the mail.

2. Originator Fields

WARNING: The standard allows only a subset of the combinations possible with the From, Sender, 

              and  Reply-To  fields.   The   limitation   is
              intentional.

a. From

This field contains the identity of the person(s) who wished this message to be sent. The message-creation process should default this field to be a single machine address, indicating the AGENT (person or process) entering the message. If this is NOT done, the "Sender" field MUST be present; if this IS done, the "Sender" field is optional.

b. Sender

This field contains the identity of the AGENT (person or process) who sends the message. It is intended for use when the sender is not the author of the message, or to indicate who among a group of authors actually sent the message. If the contents of the "Sender" field would be completely redundant with the "From" field, then the "Sender" field need not be present and its use is discouraged (though still legal); in particular, the "Sender" field MUST be present if it is NOT the same as the "From" Field. 

    The  Sender  host-phrase  includes  a   phrase   which   must
    correspond  to  a  specific  agent  (i.e.,  a human user or a
    computer program)  rather  than  a  standard  address.   This
    indicates  the  expectation  that the field will identify the
    single AGENT (person or process) responsible for sending  the
IV. Semantics
A. Address Fields

mail and not simply include the name of a mailbox from which the mail was sent. For example in the case of a shared login name, the name, by itself, would not be adequate. The phrase part of the host-phrase, which refers to this agent, is expected to be a computer system term, and not (for example) a generalized person reference which can be used outside the network text message context.

Since the critical function served by the "Sender" field is the identification of the agent responsible for sending mail and since computer programs cannot be held accountable for their behavior, is strongly recommended that when a computer program generates a message, the HUMAN who is responsible for that program be referenced as part of the "Sender" field host-phrase.

c. Reply-To

This field provides a general mechanism for indicating any mailbox(es) to which responses are to be sent. Three typical uses for this feature can be distinguished. In the first case, the author(s) may not have regular machine-based mailboxes and therefore wish(es) to indicate an alternate machine address. In the second case, an author may wish additional persons to be made aware of, or responsible for, responses; responders should send their replies to the "Reply-To" mailbox(es) listed in the original message. A somewhat different use may be of some help to "text message teleconferencing" groups equipped with automatic distribution 

    services:   include  the  address  of  that  service  in  the
    "Reply-To"  field  of   all   messages   submitted   to   the
    teleconference;  then  participants can "reply" to conference
    submissions to guarantee  the  correct  distribution  of  any
    submission of their own.

Reply-To fields are NOT required to contain any machine addresses (i.e., host-phrases). Note, however, that the absence of even one valid network address will tend to prevent software systems from automatically assisting users in conveniently responding to mail.

NOTE: For systems which automatically generate address lists for
replies to messages, the following recommendations are made:

IV. Semantics
A. Address Fields

(Extensive examples are provided in Section V.) This
recommendation is intended only for originator-fields and is not
intended to suggest that replies should not also be sent to the
other recipients of this message. It is up to the respective
mail handling programs to decide what additional facilities will
be provided.

3. Receiver Fields

a. To

This field contains the identity of the primary recipients of the message.

b. cc

This field contains the identity of the secondary recipients of the message.

b. Bcc

This field contains the identity of additional recipients of the message. The contents of this field are not included in copies of the message sent to the primary and secondary recipients. Some systems may choose to include the text of the "Bcc" field only in the author(s)'s copy, while others may also include it in the text sent to all those indicated in the "Bcc" list.

B. REFERENCE SPECIFICATION FIELDS

1. Message-ID

This field contains a unique identifier (the phrase) 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 a new message identifier.

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 mach-id specification format.

IV. Semantics
B. Reference Specification Fields

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 mach-id specification format.

4. Keywords

This field contains keywords or phrases, separated by commas.

C. OTHER FIELDS AND SYNTACTIC ITEMS

1. Subject

The "Subject" field is intended to provide as much information as
necessary to adequately summarize or indicate the nature of the
message.

2. Comments

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

3. Extension-field

A relatively limited number of common fields have been defined in
this document. As network mail requirements dictate, additional
fields may be standardized. The authors of this document will
regulate the publishing of such definitions as extensions to the
basic specification.

4. User-defined-field

Individual users of network mail are free to define and use
additional header fields. Such fields must have names which are
not already used in the current specification or in any
definitions of extension-fields, and the overall syntax of these
user-defined-fields must conform to this specification's rules
for delimiting and folding fields. Due to the extension-field
publishing process, the name of a user-defined-field may be pre-
empted.

IV. Semantics
D. Dates

D. DATES AND TIMES

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

Time zone may be indicated in several ways. The military
standard uses a single character for each zone. "Z" is
Greenwhich Mean 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 GMT; the other
uses common 3-character strings for indicating time zones in
North America.

V. Examples
A. Addresses

V. EXAMPLES

A. ADDRESSES

1. Alfred E. Neuman <Neuman at BBN-TENEXA>

2. Neuman@BBN-TENEXA

These two "Alfred E. Neuman" examples have identical semantics,
as far as the operation of the local host's mail sending
(distribution) program (also sometimes called its "mailer") and
the remote host's FTP server are concerned. In the first
example, the "Alfred E. Neuman" is ignored by the mailer, as
"Neuman at BBN-TENEXA" completely specifies the recipient. The
second example contains no superfluous information, and, again,
"Neuman@BBN-TENEXA" is the intended recipient.

3. Al Neuman at BBN-TENEXA

This is identical to "Al Neuman <Al Neuman at BBN-TENEXA>". That
is, the full phrase, "Al Neuman", is passed to the FTP server.
Note that not all FTP servers accept multi-word identifiers; and
some that do accept them will treat each word as a different
addressee (in this case, attempting to send a copy of the message
to "Al" and a copy to "Neuman").

4. "George Lovell, Ted Hackle" <Shared-Mailbox at Office-1>

This form might be used to indicate that a single mailbox is
shared by several users. The quoted string is ignored by the
originating host's mailer, as "Shared-Mailbox at Office-1"
completely specifies the destination mailbox.

4. Wilt (the Stilt) Chamberlain at NBA

The "(the Stilt)" is a comment, which is NOT included in the
destination mailbox address handed to the originating system's
mailer. The address is the string "Wilt Chamberlain", with
exactly one space between the first and second words. (The
quotation marks are not included.)

V. Examples
B. Address Lists

B. ADDRESS LISTS

Gourmets: Pompous Person <WhoZiWhatZit at Cordon-Bleu>, Cooks: Childs at WGBH, Galloping Gourmet at
ANT (Australian National Television);, Wine Lovers: Cheapie at Discount-Liquors,
Port at Portugal;;,
Jones at SEA

This group list example points out the use of comments, the
nesting of groups, and the mixing of addresses and groups. Note
that the two consecutive semi-colons preceding "Jones at SEA"
mean that Jones is NOT a member of the Gourmets group.

C. ORIGINATOR ITEMS

1. Author-sent

George Jones logs into his Host as "Jones". He sends mail
himself.

From: Jones at Host

or
From: George Jones <Jones at Host>

2. Secretary-sent

George Jones logs in as Jones on his Host. His secretary, who
logs in as Secy on Shost sends mail for him. Replies to the mail
should go to George, of course.

    From:    George Jones <Jones at Host>
    Sender:  Secy at SHost

3. Shared directory or unrepresentative directory-name

George Jones logs in as Group at Host. He sends mail himself;
replies should go to the Group mailbox.

From: George Jones <Group at Host>

V. Examples
C. Originator Items

4. Secretary-sent, for user of shared directory

George Jones' secretary sends mail for George in his capacity as
a member of Group while logged in as Secy at Host. Replies
should go to Group.

    From:   George Jones<Group at Host>
    Sender: Secy at Host

Note that there need not be a space between "Jones" and the "<",
but adding a space enhances readability (as is the case in other
examples).

5. Secretary acting as full agent of author

George Jones asks his secretary (Secy at Host) to send a message
for him in his capacity as Group. He wants his secretary to
handle all replies.

    From:     George Jones <Group at Host>
    Sender:   Secy at Host
    Reply-To: Secy at Host

6. Agent for user without online mailbox

A non-ARPANET user friend of George's, Sarah, is visting.
George's secretary sends some mail to a friend of Sarah in
computer-land. Replies should go to George, whose mailbox is
Jones at Host.

    From:     Sarah Friendly
    Sender:   Secy at Host
    Reply-To: Jones at Host

7. Sent by member of a committee

George is a member of a committee. He wishes to have any replies
to his message go to all committee members.

    From:     George Jones
    Sender:   Jones at Host
    Reply-To: Big-committee: Jones at Host,
                             Smith at Other-Host,
                             Doe at Somewhere-Else;

Note that if George had not included himself in the enumeration
of Big-committee, he would not have gotten an implicit reply; the
presence of the "Reply-to" field SUPERSEDES the sending of a
reply to the person named in the "From" field.
V. Examples
C. Originator Items

8. Example of INCORRECT use

George desires a reply to go to his secretary; therefore his
secretary leaves his mailbox address off the "From" field,
leaving only his name, which is not, itself, a mailbox address.

         From:   George Jones
         Sender: Secy at SHost

THIS IS NOT PERMITTED. Replies are NEVER implicitly sent to the
"Sender"; George's secretary should have used the "Reply-To"
field, or the mail creating program should have forced the
secretary to.

9. Agent for member of a committee

George's secretary sends out a message which was authored jointly
by all the members of the "Big-committee".

         From:   Big-committee: Jones at Host,
                                Smith at Other-Host,
                                Doe at Somewhere-Else;
         Sender: Secy at SHost

D. COMPLETE HEADERS

1. Minimum required:

Date: 26 August 1976 1429-EDT
From: Jones at Host

2. Using some of the additional fields:

Date: 26 August 1976 1430-EDT
From:George Jones<Group at Host>
Sender:Secy at SHOST
To:Al Neuman at Mad-Host,
Sam Irving at Other-Host
Message-ID: <some string at SHOST>

V. Examples
D. Complete Headers

3. About as complex as you're going to get:

       Date     :  27 Aug 1976 0932-PDT
       From     :  Ken Davis <KDavis at Other-Host>
       Subject  :  Re: The Syntax in the RFC
       Sender   :  KSecy at Other-Host
       Reply-To :  Sam Irving at Other-Host
       To       :  George Jones <Group at Host>,
                   Al Neuman at Mad-Host
       cc       :  Important folk:
                   Tom Softwood <Balsa at Another-Host>,
                   Sam Irving at Other-Host;,
                   Standard Distribution::Include:
                    </main/davis/people/standard at Other-Host,
                     "<Jones>standard.dist.3" at Tops-20-Host>,
                   (The following Included Postal list is part
                   of Standard Distribution.)
                   :Postal::Include: Non-net-addrs@Other-host;,
                   :Postal: "Sam Irving, P.O. Box 001, Las Vegas,
                             Nevada"  (So that he can stay
                             apprised of the situation)
       Comment  :  Sam is away on business. He asked me to handle
                   his mail for him.  He'll be able to provide  a
                   more  accurate  explanation  when  he  returns
                   next week.
       In-Reply-To: <some string at SHOST>
       Special (action):  This is a sample of multi-word field-
                   names, using a range of characters.  There
                   could also be a field-name "Special (info)".
       Message-ID: <4231.629.XYzi-What at Other-Host>

Appendix
A. Alphabetical Listing of Syntax Rules

APPENDIX

A. ALPHABETICAL LISTING OF SYNTAX RULES

address = host-phrase / quoted-string
            / (*phrase "<" #address ">" )
            / (*phrase ":" #address ";" )
            / (":" ("Include" / "Postal" / atom) ":" address)
ALPHA       =  <any TELNET ASCII alphabetic character>
atom        =  1*<any CHAR except specials and CTLs>

CHAR = <any TELNET ASCII character>
comment = "(" *(ctext / comment / quoted-pair) ")"
CR = <TELNET ASCII carriage return>
CRLF = CR LF
ctext = <any CHAR excluding "(", ")", CR, LF and
including linear-white-space>
CTL = <any TELNET ASCII control character and DEL>

date = 1*2DIGIT ["-"] month ["-"] (2DIGIT /4DIGIT)
date-field = "Date" ":" date-time
date-time = [ day-of-week "," ] date time
day-of-week = "Monday" / "Mon" / "Tuesday" / "Tue"
            /  "Wednesday" / "Wed"  / "Thursday"  / "Thu"
            /  "Friday"    / "Fri"  / "Saturday"  / "Sat"
            /  "Sunday"    / "Sun"
delimiters = specials / comment / linear-white-space
DIGIT = <any TELNET ASCII digit>

extension-field = <Any field which is defined in a document
published as a formal extension to this
specification>

field = field-name ":" [ field-body ] CRLF

fields = date-field originator-fields *optional-field
field-body = field-body-contents
[CRLF LWSP-char field-body]
field-body-contents = <the TELNET ASCII characters making up the
field-body, as defined in the following sections, and consisting of combinations of atom, quoted- string, and specials tokens, or else consisting of texts>
field-name = fnatom *(LWSP-char [fnatom])
fnatom = 1*<any CHAR, excluding CTLs, SPACE, and ":">

Appendix
A. Alphabetical Listing of Syntax Rules

host-indicator = 1*( ("at" / "@") node )
host-phrase = phrase host-indicator
hour = 2DIGIT [":"] 2DIGIT [ [":"] 2DIGIT ]
HTAB = <TELNET ASCII horizontal-tab>

LF = <TELNET ASCII linefeed>
linear-white-space = 1*([CRLF] LWSP-char)
LWSP-char = SPACE / HTAB

mach-id = "<" host-phrase ">"
mailbox = host-phrase / (phrase mach-id)
message = fields *(CRLF *text)
month = "January" / "Jan" / "February" / "Feb"
            /  "March"     / "Mar"  / "April"     / "Apr"
            /  "May"                / "June"      / "Jun"
            /  "July"      / "Jul"  / "August"    / "Aug"
            /  "September" / "Sep"  / "October"   / "Oct"
            /  "November"  / "Nov"  / "December"  / "Dec"

node = word / 1*DIGIT

optional-field =
               "To"         ":" #address
            /  "cc"         ":" #address
            /  "bcc"        ":" #address
            /  "Subject"    ":" *text
            /  "Comments"   ":" *text
            /  "Message-ID" ":" mach-id
            /  "In-Reply-To"":" #(phrase / mach-id)
            /  "References" ":" #(phrase / mach-id)
            /  "Keywords"   ":" #phrase
            /  extension-field
            /  user-defined-field
originator-fields =
               (  "From"     ":" mailbox
                 ["Reply-To" ":" #address] )
            /  (  "From"     ":" 1#address
                  "Sender"   ":" mailbox
                 ["Reply-To" ":" #address] )

phrase = 1*word

quoted-pair = "\" CHAR
quoted-string = <"> *(qtext / quoted-pair) <">
qtext = <any CHAR except <">, CR, or LF and including
linear-white-space>
SPACE = <TELNET ASCII space>
specials = "(" / ")" / "<" / ">" / "@"/ "," / ";" / ":"
            /  "\" / <">

text = <any CHAR, including bare CR and/or bare LF, but
NOT including CRLF>
Appendix
A. Alphabetical Listing of Syntax Rules

time = hour zone

user-defined-field = <Any field which has not been defined in
this specification or published as an extension to this specification; names for such fields must be unique and may be preempted by putlished
extensions>

word = atom / quoted-string

zone = ( ("+" / "-") 4DIGIT )
            / ( ["-"] (1ALPHA
              / "GMT" / "NST"  / "AST" / "ADT" / "EST" / "EDT"
              / "CST" / "CDT"  / "MST" / "MDT" / "PST" / "PDT"
              / "YST" / "YDT"  / "HST" / "HDT" / "BST" / "BDT" ))

<"> = <TELNET ASCII quote mark>

Appendix
B. Simple Parsing

B. SIMPLE 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. They describe a limited view of
messages and are 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:

SYNTAX:

message = *field *(CRLF *text)

field = field-name ":" [field-body] CRLF

field-name = fnatom *( LWSP-char [fnatom] )

fnatom = 1*<any CHAR, excluding CTLs, SPACE, and ":">

field-body = *text [CRLF LWSP-char field-body]

SEMANTICS:

Headers occur before the message body and are terminated by

a null line (i.e., two contiguous CRLFs).

A line which continues a header field begins with a SPACE or

HTAB character, while a line beginning a field starts with a
printable character which is not a colon.

A field-name consists of one or more printable characters

(excluding colon), each separated by one or more SPACES or HTABS.
A field-name MUST be contained on one line. Upper and lower case
are not distinguished when comparing field-names.

Bibliography

BIBLIOGRAPHY

ANSI. Representations of universal time, local time
differentials, and United States time zone references for information interchange. ANSI X3.51-1975; American National Standards Institute: New York, 1975.

Bhushan, A.K. The File Transfer Protocol. ARPANET Request for
Comments, No. 354, Network Information Center No. 10596; Augmentation Research Center, Stanford Research Institute: Menlo Park, July 1972.

Bhushan, A.K. Comments on the File Transfer Protocol. ARPANET
Request for Comments, No. 385, Network Information Center No. 
   11357;  Augmentation  Research   Center,   Stanford   Research
   Institute:  Menlo Park, August 1972.

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