RFC724
From RFC-Wiki
RFC # 724 NIC #37435 12 May 1977
Proposed Official Standard for the
Format of ARPA Network Messages
by
Ken Pogran, MIT-LCS/CSR (Pogran at MIT-Multics)
John Vittal, BBN (Vittal at BBN-TENEXA)
Dave Crocker, RAND-ISD (DCrocker at Rand-Unix)
Austin Henderson, BBN (Henderson at BBN-TENEXD)
Proposed Standard for Message Format / ii
PREFACE
ARPA's Committee on Computer-Aided Human Communication (CAHCOM) wishes to promulgate an official standard for the format of ARPA Network mail headers which will adequately meet the needs of the various message service subsystems on the Network today. The authors of this RFC constitute the CAHCOM subcommittee charged with the task of developing this new standard; this document presents our current thoughts on the matter and a specific proposal.
This document is organized as follows: First, we present a history, of the development of what has become known as the ARPA Network "mail" or "message" service, and the issues which we feel are most pressing -- problems for which solutions are lacking today, inhibiting the further development of message subsystems. We then present the specification for the new ARPA Network Message Header standard. This is followed by a References section.
Essentially, we propose a revision to 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.
We would like to make clear the status of this proposed standard: The CAHCOM Steering Committee has replaced the Message Service Committee as the ARPANET standards-setting organization in the area of message services. It is expected that the proposal of this CAHCOM subcommittee, when in its final form, will be adopted as an ARPANET standard by CAHCOM. In the interests of making this standard the best possible one, we are distributing this proposal as an RFC.
Please send any comments and criticisms to any of the authors of this RFC by 15 June 1977. It is planned that the standard will be officially adopted by 1 September 1977, with hosts expected to accept its syntax by 1 January 1978.
Proposed Standard for Message Format / iii
CONTENTS
I. PROBLEMS WITH ARPANET
MESSAGE STANDARDS
A. Background and History
B. Issues and Conclusions
C. Message Parts
D. Adoption of the Standard
II. STANDARD FOR THE FORMAT
OF ARPA NETWORK MESSAGES
A. Framework
B. Syntax
C. Semantics
D. Examples
III. REFERENCES
APPENDIX
A. Alphabetical Listing of Syntax Rules
I. Problems with ARPANET Message Standards / 1 A. Background and History
I. PROBLEMS WITH ARPANET MESSAGE STANDARDS
A. BACKGROUND AND HISTORY
Today's ARPA Network "mail" or "message" service uses, for its delivery mechanism, two special commands of the File Transfer Protocol. Viewed from within the structure of FTP, the entire message, both header and text, is data for the FTP MAIL and MLFL commands. This facility was added to the File Transfer Protocol as an afterthought; it was an interim solution to be used only until a separate mail transmission protocol was specified. Several versions of such a protocol have been proposed, but none has yet received general acceptance. Meanwhile, attempts have been made to improve upon the original interim facility.
As message service subsystems on various host systems (especially TENEX) developed to the point where rudimentary parsing of incoming messages was being done, it became clear that it would be desirable to standardize the format and content of the headers of messages transmitted between hosts using these FTP commands. To this end, an ad hoc committee wrote RFC 561, which suggested a standard message header format. The committee was unofficial, so it could not legislate a standard, it could only recommend. However, the standard it suggested adequately met an urgent need, and was generally adopted.
Several salient points should be noted:
1. RFC 561 defined the concept of a message header, and specified the syntax which delimited it from the actual text of a message;
2. It proposed a standard format for the most obvious and
most urgently-needed header items: "From:", "Date:", and
"Subject:";
3. It proposed that a general standard syntax be used for
all other header items;
4. RFC 561 is still, today, an unofficial standard, adhered to by most because of its utility;
5. Its syntax was designed to allow humans to read the text
easily, without the aid of special message processing
systems.
I. Problems with ARPANET Message Standards / 2 A. Background and History
As message services grew in sophistication, the need for specific header items in RFC 561's "miscellaneous" category grew: "To:" and "cc:", especially, were generated and recognized by several different message services. However, there was no specific standard for the syntax of the contents of these items. The message service subsystems on TENEX developed a particular format for these items; since more messages originated from the TENEX hosts on the Network than from any other type of host system, the TENEX format for these fields soon became a de facto standard. Message service subsystems on TENEX began to parse these fields, expecting them to be in the TENEX-generated format. Message service subsystems on other hosts -- Multics, for example -- began to dabble with other formats for these fields, since there was no standard for them, only to receive complaints from users of TENEX message service subsystems that their "non- standard" message headers could not be parsed according to the (de facto) "standard" syntax.
Recognizing that the time had come to make an attempt to standardize the additional header fields that had come into use since RFC 561 was published, ARPA's Message Service Committee chartered a small group in 1975 to develop a revised version of RFC 561 which would define the syntax of these additional message header fields. Several things should be noted about this small group of people: first, they were TENEX-oriented; when the functionality of the message header items they desired was matched by the functionality of an already-existing message header item of the TENEX message subsystems, they adopted the syntax used by the TENEX message subsystems. Second, they based additional header items not already found on TENEX message subsystems on the deliberations of the Message Service Committee. Third, they were not familiar with the procedure for publication of a document as a Network RFC.
The document which this group produced, labelled RFC 680, "Message Transmission Protocol", received only limited distribution. Matters were further confused because its title was misleading, since it was not a protocol for the transmission of messages between ARPA Network hosts, but rather a standard for the format of messages transmitted via the standard File Transfer Protocol. Some, including the Message Service Committee, believed that RFC 680 became a Network Standard. This was not strictly true, because it never received proper distribution, and it had never been "officially blessed" by anyone, to turn it from a request for comments into an accepted official ARPA Network standard document. Reflecting this confusion over the status of the document are the facts that the document DOES currently reside in the "official" ARPANET Protocol Handbook, and most users and message system implementors remain unaware that this is so.
I. Problems with ARPANET Message Standards / 3 A. Background and History
For all its shortcomings, RFC 680 has performed a needed service, just as did RFC 561 before it. It defined additional message header items at a time when this needed to be done. Unfortunately, since the group had not sought ideas and input from others, the specification did not adequately respond to a sufficient set of community needs. In addition, the manner in which the document was promulgated -- or not promulgated -- left a great deal to be desired. Implementators of message-processing subsystems who had not received RFC 680 proceeded to go their own ways, feeling justified in doing so, while those who accepted RFC 680 as a standard felt justified in complaining to -- and about -- those whom they considered to be maverick implementors of idiosyncratic message service subsystems.
Perhaps because of the ad-hoc nature of the interim mail facility, users have not, until recently, attempted to push the system to the limits of their imagination. Presently, however, several different sites are using the "interim" mail facility for more than it was designed and in ways which are incompatible both with each other and with the original intent of the facility. Mail subsystem implementors are increasingly being asked to provide for the handling of mail from idiosyncratic hosts. Also, it has become clear that there are a few very specific features, too useful to ignore, which cannot reasonably be specified within the syntax of RFC 680.
B. ISSUES AND CONCLUSIONS
At first glance, it would seem that a resolution of today's somewhat chaotic situation could best be obtained by immediately junking the existing "interim" mail facility, and adopting a true mail transmission protocol. We strongly believe that this would be ill-advised at this time, for we feel that there is no general understanding within the Network community today of how to specify and implement a full and adequate mail transmission protocol. However, we are convinced that there is, finally, a strong commitment within the Network community to attack this problem (which there was not at the time the "interim" mail transmission facility was specified and developed).
The frontal attacks on the mail protocol problem have, so far, resulted in at least two suggestions for a mail transmission protocol. Why should not one of these protocols be adopted immediately? We feel that, in general, there has been a tendency for experimental Network software to be prematurely treated as though it were adequately designed and fully operational. Typically, the system or protocol proposed is so much better than what was previously available that its experimental nature is disregarded, and it is pressed into service before it has had a
I. Problems with ARPANET Message Standards / 4 B. Issues and Conclusions
chance to properly develop and mature. We are very concerned that this phenomenon not afflict the Network mail system any more than it already has.
While it is true that there are several sites in the ARPA Community which have mail systems that understand the syntax specified in RFC's 561 and 680, in addition to some of the "non- standard" syntax provided by the mail generating programs at several other sites, most mail systems do not parse much of the contents of received messages. A consideration of the syntax specified here is that messages which are sent to people should be easily read by people. Parsers which can turn an ugly, syntactically expedient form into something which is easy to read are the exception, rather than the rule, in today's message systems. Also, the modifications to the existing "non-standard" syntax should be kept to a minimum, enhancing the probability that the requirement of small perturbations to existing software will be accepted.
With this syntax, we introduce mechanisms so that:
1. Users of mail systems can have multiple mailboxes, either
on one machine or multiple machines, all of which are
treated identically; the default mailbox for a user is
not necessarily associated (directly) with his login
name.
2. Mail for a person can be sent to other than a single,
default mailbox.
3. Named groups may consist of both individuals and
(possibly) other named groups (i.e., nesting within
groups is permitted).
4. Address lists may contain references to other, stored,
lists. The complete path with which one can retrieve the
stored list may be specified in order to allow either
manual or automatic retrieval of the stored list.
5. Address lists may contain references to addresses which
are not accessible through the standard ARPANET message
system. For example, U.S. Postal system addresses can
be specified. Such addresses are, of course, expected to
be ignored by the ARPANET system, although individual
sites may provide services for using the information
(e.g., automatically sending a copy of the message to a
line printer, in preparation for transmission through the
Postal system).
6. Parenthetical remarks, or comments, can be included and
syntactically recognized as such within some header
items.
I. Problems with ARPANET Message Standards / 5 B. Issues and Conclusions
7. Received messages are capable of being read by humans
without a program having to parse the message (or parts
of it) before presenting the message to the user; however
there is sufficient formal syntax to enable a parsing
program to modify the appearance and content of material
presented to users. Although message-display software
may exercise considerable control over message
appearance, the degree to which a message's actual format
is PLEASANT for humans to read is entirely the
responsibility of the message creation program.
No mechanism for authentication is provided, since the Network provides no mechanisms for enforcing mail security. The syntax does provide for one aspect of "correctness": a distinction is made between an address which is claimed to be a valid network address and one which is simply free text, included for the convenience of the human participants.
C. MESSAGE PARTS
Some confusion has existed over the roles played by different message parts. Einar Stefferud has suggested using the perspective of envelope, letter head, and letter content. The presence of structured portions in messages additionally requires reference to "headers".
In computer-based message systems, human users do not generally encounter "envelopes", which are often constructed automatically, to be used by the participating system(s) to deliver the message. For example on TENEX, the envelope is the name of the file containing a message awaiting transmission. For FTP servers, it is the data portion of the MAIL or MLFL command line. Some systems attach "envelope-like" information to the message header, such as time-stamp and originating host name.
In paper-based communications, headers occur both before (e.g., "To:" and "From:" and after (e.g., "cc:" and "enclosure:") the body of the message. Within this standard, all headers occur before the body of the message, although local message display programs may choose to alter that ordering.
Wayne Hathaway has pointed out that ARPANET message format does not support specification of letterheads, since these are a type of organizational public relations symbol. Some idiosyncrasies are supported, however, by way of choosing special field names.
In general, it is important to realize that the header portion of a message plays several roles during the life of a
I. Problems with ARPANET Message Standards / 6 C. Message Parts
message, variously participating in each of the three functions suggested by Stefferud.
D. ADOPTION OF THE STANDARD
During the early phases of specifying this standard, a great deal of concern was expressed over the problems which may be experienced during the transition from the current standard to this new one. We feel that the true problem is the lack of realization that THERE IS NO CURRENT OFFICIAL STANDARD. Enough systems have enough overlapping behaviors to allow the current mail environment to function, but this in no way constitutes a standard.
In fact, we strongly believe that the new requirements imposed by the proposed standard involve less complexity than the ambiguities resulting from the current variations in system behaviors.
II. Standard for the Format of Messages / 7
II. STANDARD FOR THE FORMAT
OF ARPA NETWORK MESSAGES
This standard supercedes 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 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. Certain equivalences are defined, such as between a space character <space> and an end-of-line character <crlf>, which both facilitate the formal specification and indicate what the OFFICIAL semantics are for messages. Particular implementations may wish to preserve further distinctions which the specification does not require.
A. 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, of this standard.
Messages are expected to consist of lines of text. No special provisions are made, at this time, for encoding drawings, facimile, 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
II. Standard for the Format of Messages / 8 A. Framework
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. 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. Our approach is similar
to that of the TELNET protocol, in that we are defining a basic
standard which includes a mechanism for (optionally) extending
itself. The authors of this document will regulate the
publishing of specifications for these extensions.
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. Relative to paper-based communication, it is interesting to note that the 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 capabilties of their individual message systems.
II. Standard for the Format of Messages / 9 B. Syntax
B. SYNTAX
This syntax is given in four parts. The first part describes a base-level lexical analyzer which feeds the higher- level parser described in the succeeding sections. The second part gives a general syntax for messages and standard header fields. The third part specifies the syntax of addresses. A final section specifies some general syntax which supports the other sections.
1. LEXICAL ANALYSIS OF MESSAGES
a. General Description
A message consists of headers and, optionally, a body (i.e.
the <message-text>). The <message-text> part is just a
sequence of ASCII characters; it is separated from the
headers by a null line (i.e., a line with nothing preceding
the <crlf>).
1) Folding and unfolding of headers
Each header item can be viewed as a single, logical, long
line of ASCII characters. For convenience, 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> characters, you
can instead insert a <crlf> immediately followed by AT
LEAST one <linear-white-space> character. 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
II. Standard for the Format of Messages / 10 B. Syntax 1. Lexical Analysis
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
<linear-white-space-char> as equivalent to the <linear-
white-space-char>.
2) 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 decimal values between 33 and 126)
and <linear-white-space> characters. The <field-body> may
composed of any ASCII characters (other than <cr> and
<lf>, which have been removed by unfolding).
Certain 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 addresses.
Other fields, such as the subject field, are regarded
simply as a single line of text.
3) Field names
To aid in the creation and reading of <field-name>s, the
free insertion of <linear-white-space> characters is
allowed in reasonable places. Rather than obscuring the
syntax specification for <field-name> with the explicit
syntax for these <linear-white-space> characters, the
existence of a simple "lexical" analyzer is assumed. The
analyzer reinterprets the unfolded text which comprises
the <field-name> as a sequence of <atoms> separated by
<linear-white-space> characters. The field name may be
conveniently represented by the sequence of these atoms,
separated by a single ASCII space character.
II. Standard for the Format of Messages / 11 B. Syntax 1. Lexical Analysis
4) Field bodies
To aid in the creation and reading of structured fields,
the free insertion of <linear-white-space> characters is
allowed in reasonable places. Rather than obscuring the
syntax specifications for these structured fields with
explicit syntax for these <linear-white-space> characters,
the existence of another simple "lexical" analyzer is
assumed. It provides an interpretation of the unfolded
text comprising the body of the field as a sequence of
lexical symbols. These include
- individual special characters
- quoted strings
- comments
- atoms
The first three symbols are self-delimiting. Atoms are
not; they therefore are delimited by the self-delimiting
symbols and by <linear-white-space>.
So, for example, the folded body of an address field
":sysmail"@ Some-Host,
Muhammed(I am the greatest)Ali at 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
WBA atom
b. Formal Definition
<field> ::= <field-name> ":" <field-body>
<field-name> ::= <atom>
| <atom> <field-name>
<field-body> ::= <field-body-contents>
| <field-body-contents> <crlf>
<linear-white-space-char>
<field-body>
II. Standard for the Format of Messages / 12 B. Syntax 1. Lexical Analysis
<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>, <text-line>,
and <specials> tokens>
<atom> ::= <a sequence of one or more TELNET
ASCII alpha-numeric or graphics
characters, excluding all control
characters (those characters with
a decimal value less than 33 or
equal to 127) and <delimeters> >
<quoted-string> ::= <double quote mark ("), decimal 34>
<a sequence of one or more TELNET
ASCII characters, where two
adjacent quotes are treated as a
single quote and part of the
string> <">
<text-line> ::= <a sequence of one or more TELNET
ASCII characters excluding <cr>
and <lf> >
<message-text> ::= <a sequence of zero of more TELNET
ASCII characters>
<delimeters> ::= <specials> | <comment>
| <linear-white-space> | <crlf>
<specials> ::= "(" | ")" | "<" | ">"
| "@" | "," | ";" | ":" | <">
<comment> ::= "(" <TELNET ASCII characters, except
<crlf> > ")"
<linear-white-space>::= <linear-white-space-char>
| <linear-white-space-char>
<linear-white-space>
<linear-white-space-char>::= <space> | <horizontal-tab>
<space> ::= <TELNET ASCII space (decimal 32)>
<tab> ::= <TELNET ASCII tab (decimal 9)>
<cr> ::= <TELNET ASCII carriage return
(decimal 13)>
<lf> ::= <TELNET ASCII line feed (decimal 10)>
<crlf> ::= <TELNET ASCII carriage return/line
feed (decimal 13, followed by
decimal 10)>
II. Standard for the Format of Messages / 13 B. Syntax 1. Lexical Analysis
c. Clarifications
1) Comments
Comments may appear only within <field-body>s of
structured fields. A comment is any set of TELNET ASCII
characters, which is not within a quoted string, and which
is enclosed in matching parentheses; parentheses nest, so
that if a left paren occurs in a comment string, there
must also be a matching right paren.
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.
2) "White space"
Remember that in structured fields, MULTIPLE LINEAR WHITE
SPACE TELNET ASCII CHARACTERS (namely <tab>s and <space>s)
ARE TREATED AS SINGLE SPACES AND MAY FREELY SURROUND ANY
SYMBOL. In all header fields, at least one <space> is
REQUIRED only at the beginning of folded lines.
Writers of mail-sending (i.e. header generating) programs
should realize that there is no Network-wide definition of
the effect of <tab> TELNET ASCII characters on the
appearance of text at another Network host; therefore, the
use of <tab>s in message headers, though permitted, is
discouraged.
Note that the contents of messages are required to conform
with TELNET NVT conventions (e.g. <cr> must be followed
by either <lf>, making a <crlf>, or <null>, if the <cr> is
to stand alone).
3) Quoted strings
Where permitted (i.e., in structured fields) quoted
strings are treated as a single symbol (i.e. equivalent
to an <atom> syntactically). However, if quoted strings
are to be "folded" onto multiple lines, then the syntax
for folding must be adhered to (See items II.B.1.a.1,
above, and II.B.1.c.6, below.) Note that the official
semantics do not encounter <crlf>s in quoted strings,
although particular parsing programs may wish to note
their presence.
II. Standard for the Format of Messages / 14 B. Syntax 1. Lexical Analysis
4) Bracketing characters
There are two types of brackets which must be well nested:
- Parentheses are used to indicate comments.
- Angle brackets ("<" and ">") are used
where there is a question of the presence
of machine-usable code (e.g. deliminating
mailboxes).
5) Case independence of certain specials <atom>s
It should be assumed by all mail reading programs that
certain <atom>s can be represented in any combination of
upper and lower case. These are:
- <field-name>s,
- "File", in a <path>,
- "at", in an <at-indicator>,
- <host-name>s,
- <day-of-week>s,
- <string-month>s, and
- <time-zone>s
For example, the <field-name>s "From", "FROM", "from", and
even "FroM" should all be treated identically. Note that,
at the level of this specification, case IS relevant to
other <word>s and <text-line>s. Also see Section
II.C.1.a.4, below.
6) 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, and 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.
7) Backspace characters
Backspace TELNET ASCII characters (ASCII BS, decimal 8)
may be included in <text-line> and <quoted-string> to
effect overstriking; however, any use of backspaces which
effects an overstrike to the left of the beginning of the
<text-line> or <quoted-string> is prohibited.
II. Standard for the Format of Messages / 15 B. Syntax 2. Messages
2. GENERAL SYNTAX OF MESSAGES:
NOTE: The syntax indicates that items in <required-headers>
must be in a specific order and precede all other header
items. Header fields, in fact, are NOT required to occur in
any particular order. Required header items must be unique
(occur exactly once). This specification permits multiple
occurrences of most optional fields. However, the
interpretation of such multiple occurrences is not specified
here.
<message> ::= <headers>
| <headers> <crlf> <message-text>
<headers> ::= <required-headers>
| <required-headers> <optional-headers>
<required-headers> ::= <date-field> <originator>
<originator> ::= <mach-from-field>
| <mach-from-list> <sender-field>
| <mach-from-field> <reply-to-field>
| <any-from-field> <sender-field>
<reply-to-field>
<date-field> ::= "Date" ":" <date-time>
<mach-from-field> ::= "From" ":" <mach-addr-item>
<mach-from-list> ::= "From" ":" <mach-addr-list>
<any-from-field> ::= "From" ":" <address-list>
<sender-field> ::= "Sender" ":" <host-phrase>
<reply-to-field> ::= "Reply-To" ":" <mach-addr-list>
<optional-headers>::= <optional-header-field>
| <optional-headers>
<optional-header-field>
<optional-header-field> ::= <addressee-field>
| <extension-field>
<addressee-field> ::= "To" ":" <address-list>
| "cc" ":" <address-list>
| "bcc" ":" <address-list>
| "Fcc" ":" <path-list>
<extension-field> ::= "In-Reply-To" ":" <reference-list>
| "Keywords" ":" <phrase-list>
| "Message-Id" ":" <mach-host-phrase>
| "References" ":" <reference-list>
| "Subject" ":" <text-line>
| "Comments" ":" <text-line>
| <user-defined-field>
II. Standard for the Format of Messages / 16 B. Syntax 2. Messages
<user-defined-field> ::= <A <field> which has a <field-name>
not defined in this specification>
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.1) indicated how such long strings can be represented on more than one line in the actual transmitted message.
3. SYNTAX OF GENERAL ADDRESSEE ITEMS
<mach-addr-list> ::= <mach-addr-item>
| <mach-addr-item> "," <address-list>
<address-list> ::= <null>
| <address-item>
| <address-item> "," <address-list>
<address-item> ::= <mach-addr-item>
| <group-name> ":" <address-list> ";"
| <any-name>
| <path>
<mach-addr-item> ::= <mailbox>
| <phrase> "<" <mailbox-list> ">"
<group-name> ::= <phrase>
<any-name> ::= <quoted-string>
<mailbox-list> ::= <mailbox>
| <mailbox> "," <mailbox-list>
<mailbox> ::= <host-phrase>
<path> ::= ":" "File" ":" <path-name>
<path-name> ::= <path-item>
| "<" <path-list> ">"
<path-list> ::= <path-item>
| <path-item> "," <path-list>
<path-item> ::= <host-phrase>
II. Standard for the Format of Messages / 17 B. Syntax 4. Supporting Constructs
4. SUPPORTING SYNTAX
<reference-list> ::= <null>
| <reference-item>
| <reference-item> "," <reference-list>
<reference-item> ::= <phrase>
| <mach-host-phrase>
<mach-host-phrase>::= "<" <host-phrase> ">"
<host-phrase> ::= <phrase> <host-indicator>
<host-indicator> ::= <at-indicator> <host-name>
<at-indicator> ::= "at" | "@"
<host-name> ::= <atom>
| <decimal host address>
<date-time> ::= <day> <date>
II. Standard for the Format of Messages / 18 B. Syntax 4. Supporting Constructs
<time-zone> ::= "GMT" | "Z" | "GDT"
| "AST" | "ADT"
| "EST" | "EDT" | "CST" | "CDT"
| "MST" | "MDT" | "PST" | "PDT"
| "YST" | "YDT" | "HST" | "HDT"
<phrase> ::= <word>
| <word> <phrase>
<phrase-list> ::= <null>
| <phrase>
| <phrase> "," <phrase-list>
<word> ::= <atom>
| <quoted-string>
II. Standard for the Format of Messages / 19 C. Semantics 1. Address Fields
C. SEMANTICS
1. ADDRESS FIELDS
a. General
1) <path>s are used to refer to a location, on the ARPANET,
containing a stored address list. The <phrase> 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:
- the file must be accessible through the local
operating system interface (if it exists), given
adequate user access rights; and
- if a host has an FTP server and a user is able to
retrieve any files from the host using that server,
then the file must be accessible through FTP, using
DEFAULT transfer settings, given adequate user access
rights.
It is intended that this mechanism will allow programs to
retrieve such lists automatically.
The interpretation of a <path> follows. This is not
intended to imply any particular implementation scheme, but
is included to aid in understanding the notion of <path>s:
- The contents of the file indicated by a <path-name> is
treated as an <address-list> and is inserted as an
<address-item> in the position of the <path-name> item
in the syntax. That is, the TELNET ASCII character
string of the <path-name> or, if present, the <path-
list> containing it, is replaced by the contents of
the file to which the <path-name> refers. Therefore,
the contents of the file indicated by a <path-name>
must be syntactically self-contained and must adhere
to the full syntax prescribed herein for <address-
list>.
- <Path-item>s of a <path-list> are alternates and the
contents of ONLY ONE of them is to be included in the
resultant address list.
2) The <phrase> part of a <mailbox> is understood to be
whatever the receiving FTP Server allows (for example,
II. Standard for the Format of Messages / 20 C. Semantics 1. Address Fields
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.
A user may have several mailboxes. The use of the second
alternative of <mach-addr-item> (<phrase> "<" <mailbox-
list> ">") indicates that a copy of the message is to be
sent to EACH mailbox named.
3) <any-name> may contain any sequence of "words". This
sequence of words, used as an <address-item>, is used to
facilitate reference to non-standard (e.g. non-Network)
addresses. Such an address might be one which is
acceptable to the U.S. Postal Service.
4) The <host-name> in a <host-phrase> must be THE official
name of a Network host, or else a decimal number indicating
the Network address for that host. The USE OF NUMBERS IS
STRONGLY DISCOURAGED and is permitted only due to the
occasional necessity of bypassing local host-name tables.
The <phrase> in a <host-phrase> is intended to be
meaningful only to the indicated host. To all other hosts,
the <phrase> is treated as a literal 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.
b. 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; the permitted
alternatives have been carefully chosen
and are adequate for the purposes of this
standard.
II. Standard for the Format of Messages / 21 C. Semantics 1. Address Fields
1) 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 user entering the message; if and
only if this is done, the "Sender:" field need not be
present.
2) Sender:
This field contains the identity of the person who sends
the message. It need not be present in the header of the
message if it is the SAME as the "From:" field.
The <sender-field-body> includes a <phrase> which must
correspond to a user, rather than a standard <address-
item>, to indicate the expectation that the field will
refer to the PERSON responsible for sending the 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> (user) is a system entity, not a generalized
person reference.
3) Reply-to:
This field provides a general mechanism for indicating any
mailbox(es) to which responses are to be sent. Three
different uses for this feature can be distinguished. In
the first case, the author(s) may not have regular
machine-based mailboxes and therefore wish 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). More interesting
is a case such as text-message teleconferencing in which an
automatic distribution facility is provided and a user
submitting an "entry" for distribution only needs to send
their message to the mailbox(es) indicated in the "Reply-
to:" field.
If there is no <reply-to-field>, then the <from-field> MUST
contain AT LEAST ONE machine address. In all cases when
used and even if a <sender> field is present, the Reply-to
field must contain at least one machine address.
NOTE: For systems which automatically generate address lists
for replies to messages, the following requirements are made:
II. Standard for the Format of Messages / 22 C. Semantics 1. Address Fields
- The receiver, when replying to a message, must NEVER
automatically include the <sender-field-body> in the
reply's address list
- If the <reply-to-field> exists, then the reply should
go ONLY to the <reply-to-field-body> addressees.
(Extensive examples are provided in Section II.D.) This
recommendation is intended only for <originator-field>s and in
no way is intended to reflect that replies should not be sent,
also, to the other recipients of this message. It is up to
the respective mail handling programs as to what additional
facilities will be provided.
c. Receiver Fields
1) To:
This field contains the identity of the primary recipients
of the message.
2) cc:
This field contains the identity of the secondary
recipients of the message.
3) Bcc:
This field contains the identity of additional recipients
of the message who are to remain hidden from 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 include it in the text
sent to all those indicated in the "Bcc:" list.
4) Fcc:
This field contains the identity of any message files in
which copies of this message are being placed by the
originator. Note that the presence of this field does NOT
guarantee long-term availability of the message in any of
the indicated files.
II. Standard for the Format of Messages / 23 C. Semantics 2. Reference Specification Fields
2. REFERENCE SPECIFICATION FIELDS
a. Message-Id:
This field contains a unique identifier (the <phrase>) to
refer to this version of this message. The uniqueness of the
message identifier is guaranteed by each host. This
identifier is intended to be machine readable, and not
necessarily meaningful to humans. A message-id pertains to
exactly one instantiation of a particular message; subsequent
revisions to the message should receive new message-id's.
b. In-Reply-To:
The contents of this field identify previous correspondence
which this message answers. If message identifiers are used
in this field, they should be enclosed in angle brackets (<>).
c. References:
The contents of this field identify other correspondence which
this message references. If message identifiers are used,
they should be enclosed in angle brackets (<>).
d. Keywords:
This field contains keywords or phrases, separated by commas.
3. OTHER FIELDS AND SYNTACTIC ITEMS
a. Subject:
The "subject:" field is intended to provide as much
information as necessary to adequately summarize or indicate
the nature of the message.
b. Comments:
Permits adding text comments onto the message without
disturbing the contents of the message's body.
II. Standard for the Format of Messages / 24 C. Semantics 4. Dates
4. DATES
It is recommended that, because of differing international
interpretations, the <string-day> option be used instead of
the <slash-day> option in the specification of a <day>.
If included, <day-of-week> must be the day implied by the
<date> specification.
<Time-zones> allow reference to Greenwich and to each of the
zones in the United States. The zone references beginning
with "A" are for Atlantic time which are one hour faster than
the corresponding Eastern times. "Y" indicates Yukon time in
Alaska, which is one hour slower than the corresponding
Pacific times, and "H" indicates Hawaiian times, which are two
hours slower.
II. Standard for the Format of Messages / 25 D. Examples
D. EXAMPLES
1. ADDRESSES
a. Alfred E. Newman <Newman at BBN-TENEXA>
Newman@BBN-TENEXA
These two "Alfred E. Newman" examples have identical
semantics, as far as the operation of the local host's mailer
and the remote host's FTP server are concerned. In the first
example, the "Alfred E. Newman" is ignored by the mailer, as
"Newman at BBN-TENEXA" completely specifies the recipient.
The second example contains no superfluous information, and,
again, "Newman@BBN-TENEXA" is the intended recipient.
b. Al Newman at BBN-TENEXA
This is identical with "Al Newman<Al Newman at BBN-TENEXA>."
That is, the full <phrase>, "Al Newman", 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 "Newman").
c. "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.
d. 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.)
II. Standard for the Format of Messages / 26 D. Examples
2. ADDRESS LISTS
Gourmets: Pompous Person <WhoZiWhatZit at Cordon-Bleu>,
Cooks: Childs at WGBH, Galloping Gourmet at
ANT (Australian National Television);
Wine Lovers: Drunk 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.
3. ORIGINATOR ITEMS
a. George Jones logs into his Host as "Jones". He sends mail
himself.
From: Jones at Host
or
From: George Jones <Jones at Host>
b. George Jones logs in as Jones on his Host. His secretary, who
logs in as Secy on her Host (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
c. 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>
d. 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).
e. 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.
II. Standard for the Format of Messages / 27 D. Examples
From: George Jones <Group at Host>
Sender: Secy at Host
Reply-to: Secy at Host
f. 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
g. 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 a
reply; the presence of the "Reply-to:" field SUPERSEDES the
sending of a reply to the person named in the "From:" field.
h. (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 she was using
should have forced her to.
i. 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
II. Standard for the Format of Messages / 28 D. Examples
4. COMPLETE HEADERS
a. Minimum required:
Date: 26 August 1976 1429-EDT
From: Jones at Host
b. Using some of the additional fields:
Date 26 August 1976 1430-EDT
From: George Jones<Group at Host>
Sender: Secy at SHOST
To: Al Newman at Mad-Host,
Sam Irving at Other-Host
Message-id: some string at SHOST
c. About as complex as you're going to get:
Date: 27 Aug 1976 0932-PDT
From: Ken Davis <KDavis at Other-Host>
Sender: KSecy at Other-Host
Reply-to: Sam Irving at Other-Host
Subject: Re: The Syntax in the RFC
To: George Jones <Group at Host>,
Al Newman at Mad-Host
cc: Tom Softwood <Balsa at Another-Host>,
Sam Irving at Other-Host,
Standard Distribution:
:File:
</main/davis/people/standard at Other Host,
"<Jones>standard.dist.3" at Tops-20-Host>
In-Reply-to: <some string at SHOST>
Message-ID: 4231.629.XYzi-What at Other-Host
Comment: Sam is away on business. He asked me to handle
his mail for him today. He'll be able to
provide a more accurate explanation tomorrow
when he returns.
III. References
III. REFERENCES
--- TELNET Protocol Specification. Network Information Center
No. 18639; Augmentation Research Center, Stanford Research
Institute: Menlo Park, August 1973.
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.
Bhushan, A.K., Pogran, K.T., Tomlinson, R.S., and White, J.E.
Standardizing Network Mail Headers. ARPANET Request for
Comments, No. 561, Network Information Center No. 18516;
Augmentation Research Center, Stanford Research Institute:
Menlo Park, September 1973.
Feinler, E.J. and Postel, J.B. ARPANET Protocol Handbook.
Network Information Center No. 7104; Augmentation Research
Center, Stanford Research Institute: Menlo Park, April 1976.
(NTIS AD A003890).
McKenzie, A. File Transfer Protocol. ARPANET Request for
Comments, No. 454, Network Information Center No. 14333;
Augmentation Research Center, Stanford Research Institute:
Menlo Park, February 1973.
Myer, T.H. and Henderson, D.A. Message Transmission Protocol.
ARPANET Request for Comments, No. 680, Network Information
Center No. 32116; Augmentation Research Center, Stanford
Research Institute: Menlo Park, 1975.
Neigus, N. File Transfer Protocol. ARPANET Request for
Comments, No. 542, Network Information Center No. 17759;
Augmentation Research Center, Stanford Research Institute:
Menlo Park, July 1973.
Postel, J.B. Revised FTP Reply Codes. ARPANET Request for
Comments, No. 640, Network Information Center No. 30843;
Augmentation Research Center, Stanford Research Institute:
Menlo Park, June 1974.
Appendix / 30 Alphabetical Listing of Syntax Rules
APPENDIX
A. ALPHABETICAL LISTING OF SYNTAX RULES
<2-digit-year> ::= <two decimal digits> <4-digit-year> ::= <four decimal digits> <24-hour-time> ::= <hour> <minute>
<addressee-field> ::= "To" ":" <address-list>
| "cc" ":" <address-list>
| "bcc" ":" <address-list>
| "Fcc" ":" <path-list>
<address-item> ::= <mach-addr-item>
| <group-name> ":" <address-list> ";"
| <any-name>
| <path>
<address-list> ::= <null> | <address-item>
| <address-item> "," <address-list>
<any-from-field> ::= "From" ":" <address-list>
<any-name> ::= <quoted-string>
<at-indicator> ::= "at" | "@"
<atom> ::= <a sequence of one or more TELNET ASCII
alpha-numeric or graphics characters,
excluding all control characters
(those characters with a decimal value
less than 33 or equal to 127) and
<delimeters> >
<comment> ::= "(" <TELNET ASCII characters, except
<crlf> > ")"
<cr> ::= <TELNET ASCII carriage return (decimal 13)>
<crlf> ::= <TELNET ASCII carriage return/line feed
(decimal 13, followed by decimal 10)>
<date> ::= <string-date> | <slash-date> <date-field> ::= "Date" ":" <date-time> <date-time> ::= <day> <date>
Appendix / 31 Alphabetical Listing of Syntax Rules
| "Friday" | "Fri"
| "Saturday" | "Sat"
| "Sunday" | "Sun"
<delimeter> ::= <specials> | <comment>
| <linear-white-space> | <crlf>
<field> ::= <field-name> ":" <field-body>
<field-body> ::= <field-body-contents>
| <field-body-contents> <crlf>
<linear-white-space-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>, <text-line>, and <specials>
tokens>
<field-name> ::= <atom> | <atom> <field-name>
<group-name> ::= <phrase>
<headers> ::= <required-headers>
| <required-headers> <optional-headers>
<host-indicator> ::= <at-indicator> <host-name> <host-name> ::= <atom> | <decimal host address> <host-phrase> ::= <phrase> <host-indicator>
<hour> ::= <two decimal digits>
<lf> ::= <TELNET ASCII line feed (decimal 10)>
<linear-white-space>::= <linear-white-space-char>
| <linear-white-space-char>
<linear-white-space>
<linear-white-space-char>::= <space> | <horizontal-tab>
<mach-addr-item> ::= <mailbox> | <phrase> "<" <mailbox-list> ">"
<mach-addr-list> ::= <mach-addr-item>
| <mach-addr-item> "," <address-list>
<mach-from-field> ::= "From" ":" <mach-addr-item> <mach-from-list> ::= "From" ":" <mach-addr-list>
<mach-host-phrase>::= "<" <host-phrase> ">"
<mailbox> ::= <host-phrase> <mailbox-list> ::= <mailbox> | <mailbox> "," <mailbox-list>
<message> ::= <headers>
| <headers> <crlf> <message-text>
Appendix / 32 Alphabetical Listing of Syntax Rules
<message-text> ::= <a sequence of zero of more TELNET ASCII
characters>
<minute> ::= <two decimal digits>
<numeric-month> ::= <one or two decimal digits>
<optional-headers>::= <optional-header-field>
| <optional-headers> <optional-header-field>
<optional-header-field> ::= <addressee-field> | <extension-field>
<originator> ::= <mach-from-field>
| <mach-from-list> <sender-field>
| <mach-from-field> <reply-to-field>
| <any-from-field> <sender-field>
<reply-to-field>
<path> ::= ":" "File" ":" <path-name> <path-item> ::= <host-phrase> <path-list> ::= <path-item> | <path-item> "," <path-list> <path-name> ::= <path-item> | "<" <path-list> ">"
<phrase> ::= <word> | <word> <phrase>
<phrase-list> ::= <null> | <phrase>
| <phrase> "," <phrase-list>
<reference-item> ::= <phrase> | <mach-host-phrase>
<reference-list> ::= <null> | <reference-item>
| <reference-item> "," <reference-list>
<quoted-string> ::= <double quote mark ("), decimal 34>
<a sequence of one or more TELNET
ASCII characters, where two adjacent
quotes are treated as a single quote
and part of the string> <">
<reply-to-field> ::= "Reply-To" ":" <mach-addr-list>
<required-headers> ::= <date-field> <originator>
<sender-field> ::= "Sender" ":" <host-phrase>
<slash-date> ::= <numeric-month> "/" <date-of-month>
"/" <2-digit-year>
<space> ::= <TELNET ASCII space (decimal 32)>
<specials> ::= "(" | ")" | "<" | ">"
| "@" | "," | ";" | ":" | <">
<string-date> ::= <day-of-month> <string-month> <string-month> ::= "January" | "Jan" | "February" | "Feb"
Appendix / 33 Alphabetical Listing of Syntax Rules
| "March" | "Mar" | "April" | "Apr"
| "May" | "June" | "Jun"
| "July" | "Jul" | "August" | "Aug"
| "September"| "Sep" | "October" | "Oct"
| "November" | "Nov" | "December" | "Dec"
<tab> ::= <TELNET ASCII tab (decimal 9)>
<text-line> ::= <a sequence of one or more TELNET ASCII
characters excluding <cr> and <lf> >
<user-defined-field> ::= <A <field> which has a <field-name> not
defined in this specification>
<word> ::= <atom> | <quoted-string>
