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TRANSLATION of the STANDARD FOR THE FORMAT OF ARPA INTERNET TEXT MESSAGES
Translated 1996 by Dick Botting.
This document revises the specifications in RFC #733, in order to serve the needs of the larger and more complex ARPA Internet. Some of RFC #733's features failed to gain adequate acceptance. In order to simplify the standard and the software that follows it, these features have been removed. A different addressing scheme is used, to handle the case of inter_network mail; and the concept of re_transmission has been introduced.
This specification is intended for use in the ARPA Internet. However, an attempt has been made to free it of any dependence on that environment, so that it can be applied to other network text message systems.
The specification of RFC #733 took place over the course of one year, using the ARPANET mail environment, itself, to provide an on_going forum for discussing the capabilities to be included. More than twenty individuals, from across the country, participated in the original discussion. The development of this revised specification has, similarly, utilized network mail_based group discussion. Both specification efforts greatly benefited from the comments and ideas of the participants.
The syntax of the standard, in RFC #733, was originally specified in the Backus_Naur Form (BNF) meta_language. Ken L. Harrenstien, of SRI International, was responsible for re_coding the BNF into an augmented BNF that makes the representation smaller and easier to understand.
This was then translated into MATHS notation and automatically formatted as a WWW page by Richard Botting.
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In this context, messages are viewed as having an envelope and contents. The envelope contains whatever information is needed to accomplish transmission and delivery. The contents compose the object to be delivered to the recipient. This standard applies only to the format and some of the semantics of message contents. It contains no specification of the information in the envelope.
However, some message systems may use information from the contents to create the envelope. It is intended that this standard facilitate the acquisition of such information by programs.
Some message systems may store messages in formats that differ from the one specified in this standard. This specification is intended strictly as a definition of what message content format is to be passed BETWEEN hosts.
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; 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.
The formal definition is divided into four levels. The bottom level describes the meta_notation used in this document. The second level describes basic lexical analyzers that feed tokens to higher_level parsers. Next is an overall specification for messages; it permits distinguishing individual fields. Finally, there is definition of the contents of several structured fields.
Messages consist of lines of text. No special provisions are made for encoding drawings, facsimile, speech, or structured text. No significant consideration has been given to questions of data compression or to transmission and storage efficiency, and the standard tends to be 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, with a format that is not specified in this document. The syntax of several fields of the rigidly_formated ("headers") section is defined in this specification; some of these fields must be included in all messages.
The syntax that distinguishes between header fields is specified separately from the internal syntax for particular fields. This separation is intended to allow simple parsers to operate on the general structure of messages, without concern for the detailed structure of individual header fields. Appendix B is provided to facilitate construction of these parsers.
In addition to the fields specified in this document, it is expected that other fields will gain common use. As necessary, the specifications for these "extension_fields" will be published through the same mechanism used to publish this document. Users may also wish to extend the set of fields that they use privately. Such "user_defined fields" are permitted.
The framework severely constrains document tone and appearance and is primarily useful for most intra_organization communications and well_structured inter_organization communication. It also can be used for some types of inter_process communication, such as simple file transfer and remote job entry. A more robust framework might allow for multi_font, multi_color, multidimension encoding of information. A less robust one, 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 with 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 capabilities of their individual message systems.
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.
Elements separated by slash ("|") are alternatives. Therefore "foo | bar" will accept foo or bar.
Elements enclosed in parentheses are treated as a single element. Thus, "(elem (foo | bar) elem)" allows the token sequences "elem foo elem" and "elem bar elem".
The character "#" preceding an element indicates repetition.
The MATHS abreviation N(element) means element #element or ` onr or more elements`.
O( and ) enclose optional elements; "O(foo bar)" is equivalent to "(foo bar|)".
A description like this
description:syntax is used to combine semanticand syntactic information into a single packet, for example
originating_site:addressshows that any address is valid, but that here it is to mean the address that orinated the message.
A construct "L(_)" is defined, similar to "#", as follows:
L(element) List of one or elements
OL(element) List of zero or elements
L12(element) List of 1 or 2 elementsindicate lists of 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 "L(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.
A double dash (--) set off some distance to the right of rule
text, starts a comment that continues to the end of line. This
is a simple way of including useful notes in parallel with the
The assertion sign '|-' is used to indicate notes
on things that follow from the rule. A kind of comment.
A message consists of header fields and, optionally, a body. The body is simply a sequence of lines containing ASCII characters. It is separated from the headers by a null line (i.e., a line with nothing preceding the CRLF).
LONG HEADER FIELDS
Each header field can be viewed as a single, logical line of ASCII characters, comprising a field_name and a field_body. For convenience, the field_body portion of this conceptual entity can be split into a multiple_line representation; this is called "folding". The general rule is that wherever there may be linear_white_space (NOT simply LWSP_chars), a CRLF immediately followed by AT LEAST one LWSP_char may instead be inserted. Thus, the single line
To: "Joe & J. Harvey" <ddd @Org>, JJV @ BBNcan be represented as:
To: "Joe & J. Harvey" <ddd @ Org>,
To: "Joe & J. Harvey"
<ddd@ Org>, JJV
To: "Joe &
J. Harvey" <ddd @ Org>, JJV @ BBNThe process of moving from this folded multiple_line representation of a header field to its single line representation is called "unfolding". Unfolding is accomplished by regarding CRLF immediately followed by a LWSP_char as equivalent to the LWSP_char.
Certain field_bodies of headers may be interpreted according to an internal syntax that some systems may wish to parse. These fields are called "structured fields". Examples include fields containing dates and addresses. Other fields, such as "Subject" and "Comments", are regarded simply as strings of text.
Field_names, unstructured field bodies and structured field bodies each are scanned by their own, independent "lexical" analyzers.
For some fields, such as "Subject" and "Comments", no structuring is assumed, and they are treated simply as texts, as in the message body. Rules of folding apply to these fields, so that such field bodies which occupy several lines must therefore have the second and successive lines indented by at least one LWSP_char.
STRUCTURED FIELD BODIES
To aid in the creation and reading of structured fields, the free insertion of linear_white_space (which permits folding by inclusion of CRLFs) is allowed between lexical tokens. Rather than obscuring the syntax specifications for these structured fields with explicit syntax for this linear_white_space, the existence of another "lexical" analyzer is assumed. This analyzer does not apply for unstructured field bodies that are simply strings of text, as described above. The analyzer provides an interpretation of the unfolded text composing the body of the field as a sequence of lexical symbols.
These symbols are:
So, for example, the folded body of an address field
":sysmail"@ Some_Group. Some_Org,
Muhammed.(I am the greatest) Ali @(the)Vegas.WBAis analyzed into the following lexical symbols and types:
:sysmail quoted string
, -- special
(I am the greatest) comment
WBA atomThe canonical representations for the data in these addresses are the following strings:
The following rules are used to define an underlying lexical analyzer, which feeds tokens to higher level parsers. See the ANSI references, in the Bibliography. [ comp.text.ASCII.html ]
Some characters are reserved for special interpretation, such
as delimiting lexical tokens. To permit use of these characters as
uninterpreted data, a quoting mechanism is provided.
To quote a character, precede it with a backslash ("\").
This mechanism is not fully general. Characters may be quoted only within a subset of the lexical constructs. In particular, quoting is limited to use within:
commentWithin these constructs, quoting is REQUIRED for CR and "\" and for the character(s) that delimit the token (e.g., "(" and ")" for a comment). However, quoting is PERMITTED for any character.
Full\ Name@Domainis not legal and must be specified as:
A comment is a set of ASCII characters, which is enclosed in
matching parentheses and which is not within a quoted_string
The comment construct permits message originators to add text
which will be useful for human readers, but which will be
ignored by the formal semantics. Comments should be retained
while the message is subject to interpretation according to
this standard. However, comments must NOT be included in
other cases, such as during protocol exchanges with mail
Comments nest, so that if an unquoted left parenthesis occurs in a comment string, there must also be a matching right parenthesis. When a comment acts as the delimiter between a sequence of two lexical symbols, such as two atoms, it is lexically equivalent with a single SPACE, for the purposes of regenerating the sequence, such as when passing the sequence onto a mail protocol server. Comments are detected as such only within field_bodies of structured fields.
If a comment is to be "folded" onto multiple lines, then the
syntax for folding must be adhered to. (See the "Lexical
Analysis of Messages" section on "Folding Long Header Fields"
above, and the section on "Case Independence" below.) Note
that the official semantics therefore do not "see" any
unquoted CRLFs that 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 that 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.
DELIMITING AND QUOTING CHARACTERS
The quote character (backslash) and characters that delimit
syntactic units are not, generally, to be taken as data that
are part of the delimited or quoted unit(s). In particular,
the quotation_marks that define a quoted_string, the
parentheses that define a comment and the backslash that
quotes a following character are NOT part of the quoted-string,
comment or quoted character. A quotation_mark that is
to be part of a quoted_string, a parenthesis that is to be
part of a comment and a backslash that 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
the ones that are not part of the alternate text group (i.e.,
ctext or qtext).
The one exception to this rule is that 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 that 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 that delimit a quoted string and backslashes that quote the following character should NOT accompany the quoted_string when the string is passed to processes that do not interpret data according to this specification (e.g., mail protocol servers).
Where permitted (i.e., in words in structured fields) quoted-strings are treated as a single symbol. That is, a quoted-string is 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 the "Lexical Analysis of Messages" section on "Folding Long Header Fields" above, and the section on "Case Independence" below.) Therefore, the official semantics do not "see" any bare CRLFs that are in quoted_strings; however particular parsing programs may wish to note their presence. For such 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.
There is one type of bracket which must occur in matched pairs and may have pairs nested within each other:
When generating these units, any mix of upper and lower case alphabetic characters may be used. The case shown in this specification is suggested for message_creating processes.
During transmission through heterogeneous networks, it may be
necessary to force data to conform to a network's local conventions. For
example, it may be required that a CR be followed either by LF, making a
CRLF, or by null, if the CR is
to stand alone). Such transformations are reversed, when the
message exits that network.
When crossing network boundaries, the message should be treated as passing through two modules. It will enter the first module containing whatever network_specific transformations that were necessary to permit migration through the "current" network. It then passes through the modules:
The "current" network's idiosyncracies are removed and the message is returned to the canonical form specified in this standard.
The "next" network's local idiosyncracies are imposed on the message.
From ==> | Remove Net_A |
Net_A | idiosyncracies |
| Impose Net_B | ==> To
| idiosyncracies | Net_B
This specification permits multiple occurrences of most fields. Except as noted, their interpretation is not specified here, and their use is discouraged.
Some systems permit mail recipients to forward a message,
retaining the original headers, by adding some new fields. This
standard supports such a service, through the "Resent-" prefix to
Whenever the string "Resent-" begins a field name, the field has the same semantics as a field whose name does not have the prefix. However, the message is assumed to have been forwarded by an original recipient who attached the "Resent-" field. This new field is treated as being more recent than the equivalent, original field. For example, the "Resent_From", indicates the person that forwarded the message, whereas the "From" field indicates the original author.
Use of such precedence information depends upon participants' communication needs. For example, this standard does not dictate when a "Resent_From:" address should receive replies, in lieu of sending them to the "From:" address.
4.3. TRACE FIELDS
Trace information is used to provide an audit trail of message handling. In addition, it indicates a route back to the sender of the message.
The list of known "via" and "with" values are registered with the Network Information Center, SRI International, Menlo Park, California.
This field is added by the final transport system that
delivers the message to its recipient. The field is intended
to contain definitive information about the address and route
back to the message's originator.
A copy of this field is added by each transport service that
relays the message. The information in the field can be quite
useful for tracing transport problems.
The names of the sending and receiving hosts and time_of_receipt may be specified. The "via" parameter may be used, to indicate what physical mechanism the message was sent over, such as Arpanet or Phonenet, and the "with" parameter may be used to indicate the mail-, or connection-, level protocol that was used, such as the SMTP mail protocol, or X.25 transport protocol.
Some transport services queue mail; the internal message identifier that is assigned to the message may be noted, using the "id" parameter. When the sending host uses a destination address specification that the receiving host reinterprets, by expansion or transformation, the receiving host may wish to record the original specification, using the "for" parameter. For example, when a copy of mail is sent to the member of a distribution list, this parameter may be used to record the original address that was used to specify the list.
4.4. ORIGINATOR FIELDS
The standard allows only a subset of the combinations possible with the From, Sender, Reply_To, Resent_From, Resent_Sender, and Resent_Reply_To fields. The limitation is intentional.
4.4.1. FROM | RESENT_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, authenticated machine
address, indicating the AGENT (person, system or process)
entering the message. If this is not done, the "Sender" field
MUST be present. If the "From" field IS defaulted this way,
the "Sender" field is optional and is redundant with the
"From" field. In all cases, addresses in the "From" field
must be machine_usable (addr_specs) and may not contain named
4.4.2. SENDER | RESENT_SENDER
This field contains the authenticated identity of the AGENT (person, system or process) that 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 mailbox specification includes a word sequence 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, system, or process) 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 local_part address unit, 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 identification of the agent responsible for sending mail and since computer programs cannot be held accountable for their behavior, it 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 mailbox specification.
4.4.3. REPLY_TO | RESENT_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, replies. 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.
This recommendation is intended only for automated use of originator_fields and is not intended to suggest that replies may not also be sent to other recipients of messages. It is up to the respective mail_handling programs to decide what additional facilities will be provided.
Examples are provided in Appendix A.
4.5. RECEIVER FIELDS
4.5.1. TO | RESENT_TO
This field contains the identity of the primary recipients of the message.
4.5.2. CC | RESENT_CC
This field contains the identity of the secondary (informational) recipients of the message.
4.5.3. BCC | RESENT_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.
4.6. REFERENCE FIELDS
4.6.1. MESSAGE_ID | RESENT_MESSAGE_ID
This field contains a unique identifier (the local_part address unit) which refers to THIS version of THIS message. The uniqueness of the message identifier is guaranteed by the host which generates it. This identifier is intended to be machine readable and not necessarily meaningful to humans. A message identifier pertains to exactly one instantiation of a particular message; subsequent revisions to the message should each receive new message identifiers.
The contents of this field identify previous correspondence which this message answers. Note that if message identifiers are used in this field, they must use the msg_id specification format.
The contents of this field identify other correspondence which this message references. Note that if message identifiers are used, they must use the msg_id specification format.
This field contains keywords or phrases, separated by commas.
4.7. OTHER FIELDS
This is intended to provide a summary, or indicate the nature, of the message.
Permits adding text comments onto the message without disturbing the contents of the message's body.
Sometimes, data encryption is used to increase the privacy of message contents. If the body of a message has been encrypted, to keep its contents private, the "Encrypted" field can be used to note the fact and to indicate the nature of the encryption. The first word parameter indicates the software used to encrypt the body, and the second, optional word is intended to aid the recipient in selecting the proper decryption key. This code word may be viewed as an index to a table of keys held by the recipient.
A limited number of common fields have been defined in this document. As network mail requirements dictate, additional fields may be standardized. To provide user_defined fields with a measure of safety, in name selection, such extension_fields will never have names that begin with the string "X-".
Names of Extension_fields are registered with the Network Information Center, SRI International, Menlo Park, California.
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
, -- hh:mm:ss zzz
, -- e.g. 20 Jun 82
If included, day_of_week must be the day implied by the date specification.
Time zone may be indicated in several ways. "UT" is Universal Time (formerly called "Greenwich Mean Time"); "GMT" is permitted as a reference to Universal Time. The military standard uses a single character for each zone. "Z" is Universal Time. "A" indicates one hour earlier, and "M" indicates 12 hours earlier; "N" is one hour later, and "Y" is 12 hours later. The letter "J" is not used. The other remaining two forms are taken from ANSI standard X3.51-1975. One allows explicit indication of the amount of offset from UT; the other uses common 3-character strings for indicating time zones in North America.
A mailbox receives mail. It is a conceptual entity which does not necessarily pertain to file storage. For example, some sites may choose to print mail on their line printer and deliver the output to the addressee's desk.
A mailbox specification comprises a person, system or process name reference, a domain_dependent string, and a name_domain reference. The name reference is optional and is usually used to indicate the human name of a recipient. The name_domain reference specifies a sequence of sub_domains. The domain_dependent string is uninterpreted, except by the final sub_domain; the rest of the mail service merely transmits it as a literal string.
A name_domain is a set of registered (mail) names. A name_domain specification resolves to a subordinate name_domain specification or to a terminal domain_dependent string. Hence, domain specification is extensible, permitting any number of registration levels.
Name_domains model a global, logical, hierarchical addressing scheme. The model is logical, in that an address specification is related to name registration and is not necessarily tied to transmission path. The model's hierarchy is a directed graph, called an in_tree, such that there is a single path from the root of the tree to any node in the hierarchy. If more than one path actually exists, they are considered to be different addresses.
The root node is common to all addresses; consequently, it is not referenced. Its children constitute "top_level" name_domains. Usually, a service has access to its own full domain specification and to the names of all top_level name_domains.
The "top" of the domain addressing hierarchy -- a child of the root __ is indicated by the right_most field, in a domain specification. Its child is specified to the left, its child to the left, and so on.
Some groups provide formal registration services; these constitute name_domains that are independent logically of specific machines. In addition, networks and machines implicitly compose name_domains, since their membership usually is registered in name tables.
In the case of formal registration, an organization implements a (distributed) data base which provides an address_to_route mapping service for addresses of the form:
Note that "organization" is a logical entity, separate from any particular communication network.
A mechanism for accessing "organization" is universally available. That mechanism, in turn, seeks an instantiation of the registry; its location is not indicated in the address specification. It is assumed that the system which operates under the name "organization" knows how to find a subordinate registry. The registry will then use the "person" string to determine where to send the mail specification.
The latter, network_oriented case permits simple, direct, attachment_related address specification, such as:
Once the network is accessed, it is expected that a message will go directly to the host and that the host will resolve the user name, placing the message in the user's mailbox.
6.2.2. ABBREVIATED DOMAIN SPECIFICATION
Since any number of levels is possible within the domain hierarchy, specification of a fully qualified address can become inconvenient. This standard permits abbreviated domain specification, in a special case:
This feature is subject to approval by local subdomains. Individual sub_domains may require their member systems, which originate mail, to provide full domain specification only. When permitted, abbreviations may be present only while the message stays within the sub_domain of the sender.
Use of this mechanism requires the sender's sub_domain to reserve the names of all top_level domains, so that full specifications can be distinguished from abbreviated specifications.
and one recipient's address is:
and another's is:
then ".registry_1.organization_X" need not be specified in the the message, but "registry_C.registry_2" DOES have to be specified. That is, the first two addresses may be abbreviated, but the third address must be fully specified.
When a message crosses a domain boundary, all addresses must be specified in the full format, ending with the top_level name_domain in the right_most field. It is the responsibility of mail forwarding services to ensure that addresses conform the relaying service must make the necessary expansions. It should be noted that it often is difficult for such a service to locate all occurrences of address abbreviations. For example, it will not be possible to find such abbreviations within the body of the message. The "Return_Path" field can aid recipients in recovering from these errors.
A domain_ref must be THE official name of a registry, network, or host. It is a symbolic reference, within a name subdomain. At times, it is necessary to bypass standard mechanisms for resolving such references, using more primitive information, such as a network host address rather than its associated host name.
To permit such references, this standard provides the domain-literal construct. Its contents must conform with the needs of the sub_domain in which it is interpreted.
Domain_literals which refer to domains within the ARPA Internet specify 32-bit Internet addresses, in four 8-bit fields noted in decimal, as described in Request for Comments #820, "Assigned Numbers." For example:
6.2.4. DOMAIN_DEPENDENT LOCAL STRING
The local_part of an addr_spec in a mailbox specification (i.e., the host's name for the mailbox) is understood to be whatever the receiving mail protocol server allows. For example, some systems do not understand mailbox references of the form "P. D. Q. Bach", but others do.
This specification treats periods (".") as lexical separators. Hence, their presence in local_parts which are not quoted_strings, is detected. However, such occurrences carry NO semantics. That is, if a local_part has periods within it, an address parser will divide the local_part into several tokens, but the sequence of tokens will be treated as one uninterpreted unit. The sequence will be re_assembled, when the address is passed outside of the system such as to a mail protocol service.
For example, the address:
is legal and does not require the local_part to be surrounded with quotation_marks. (However, "First Last" DOES require quoting.) The local_part of the address, when passed outside of the mail system, within the Registry.Org domain, is "First.Last", again without quotation marks.
6.2.5. BALANCING LOCAL_PART AND DOMAIN
In some cases, the boundary between local_part and domain can be flexible. The local_part may be a simple string, which is used for the final determination of the recipient's mailbox. All other levels of reference are, therefore, part of the domain.
For some systems, in the case of abbreviated reference to the local and subordinate sub_domains, it may be possible to specify only one reference within the domain part and place the other, subordinate name_domain references within the local_part. This would appear as:
Such a specification would be acceptable to address parsers which conform to RFC #733, but do not support this newer Internet standard. While contrary to the intent of this standard, the form is legal.
Also, some sub_domains have a specification syntax which does not conform to this standard. For example:
uses a different parsing sequence for local_part than for domain.
An individual may have several mailboxes and wish to receive mail at whatever mailbox is convenient for the sender to access. This standard does not provide a means of specifying "any member of" a list of mailboxes.
A set of individuals may wish to receive mail as a single unit (i.e., a distribution list). The group construct permits specification of such a list. Recipient mailboxes are specified within the bracketed part (":" - ";"). A copy of the transmitted message is to be sent to each mailbox listed. This standard does not permit recursive specification of groups within groups.
While a list must be named, it is not required that the contents of the list be included. In this case, the address serves only as an indication of group distribution and would appear in the form:
Some mail services may provide a group_list distribution facility, accepting a single mailbox reference, expanding it to the full distribution list, and relaying the mail to the list's members. This standard provides no additional syntax for indicating such a service. Using the group address alternative, while listing one mailbox in it, can mean either that the mailbox reference will be expanded to a list or that there is a group with one member.
6.2.7. EXPLICIT PATH SPECIFICATION
At times, a message originator may wish to indicate the transmission path that a message should follow. This is called source routing. The normal addressing scheme, used in an addr_spec, is carefully separated from such information; the route portion of a route_addr is provided for such occasions. It specifies the sequence of hosts and|or transmission services that are to be traversed. Both domain_refs and domain_literals may be used.
It often is necessary to send mail to a site, without knowing any of its valid addresses. For example, there may be mail system dysfunctions, or a user may wish to find out a person's correct address, at that site.
This standard specifies a single, reserved mailbox address (local_part) which is to be valid at each site. Mail sent to that address is to be routed to a person responsible for the site's mail system or to a person with responsibility for general site operation. The name of the reserved local_part address is:
Postmasterso that "Postmaster@domain" is required to be valid.
ANSI. "USA Standard Code for Information Interchange," X3.4. American National Standards Institute: New York (1968). Also in: Feinler, E. and J. Postel, eds., "ARPANET Protocol Handbook", NIC 7104.
ANSI. "Representations of Universal Time, Local Time Differentials, and United States Time Zone References for Information Interchange," X3.51-1975. American National Standards Institute: New York (1975).
Bemer, R.W., "Time and the Computer." In: Interface Age (Feb. 1979).
Bennett, C.J. "JNT Mail Protocol". Joint Network Team, Rutherford and Appleton Laboratory: Didcot, England.
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; SRI International: Menlo Park (September 1973).
Birrell, A.D., Levin, R., Needham, R.M., and Schroeder, M.D. "Grapevine: An Exercise in Distributed Computing," Communications of the ACM 25, 4 (April 1982), 260-274.
Crocker, D.H., Vittal, J.J., Pogran, K.T., Henderson, D.A. "Standard for the Format of ARPA Network Text Message," ARPANET Request for Comments No. 733, Network Information Center No. 41952. SRI International: Menlo Park (November 1977).
Feinler, E.J. and Postel, J.B. ARPANET Protocol Handbook, Network Information Center No. 7104 (NTIS AD A003890). SRI International: Menlo Park (April 1976).
Harary, F. "Graph Theory". Addison_Wesley: Reading, Mass. (1969).
Levin, R. and Schroeder, M. "Transport of Electronic Messages through a Network," TeleInformatics 79, pp. 29-33. North Holland (1979). Also as Xerox Palo Alto Research Center Technical Report CSL-79-4.
Myer, T.H. and Henderson, D.A. "Message Transmission Protocol," ARPANET Request for Comments, No. 680, Network Information Center No. 32116. SRI International: Menlo Park (1975).
NBS. "Specification of Message Format for Computer Based Message Systems, Recommended Federal Information Processing Standard." National Bureau of Standards: Gaithersburg, Maryland (October 1981).
NIC. Internet Protocol Transition Workbook. Network Information Center, SRI_International, Menlo Park, California (March 1982).
Oppen, D.C. and Dalal, Y.K. "The Clearinghouse: A Decentralized Agent for Locating Named Objects in a Distributed Environment," OPD_T8103. Xerox Office Products Division: Palo Alto, CA. (October 1981).
Postel, J.B. "Assigned Numbers," ARPANET Request for Comments, No. 820. SRI International: Menlo Park (August 1982).
Postel, J.B. "Simple Mail Transfer Protocol," ARPANET Request for Comments, No. 821. SRI International: Menlo Park (August 1982).
Shoch, J.F. "Internetwork naming, addressing and routing," in Proc. 17th IEEE Computer Society International Conference, pp. 72-79, Sept. 1978, IEEE Cat. No. 78 CH 1388-8C.
Su, Z. and Postel, J. "The Domain Naming Convention for Internet User Applications," ARPANET Request for Comments, No. 819. SRI International: Menlo Park (August 1982).
From: George Jones <Jones@Group.Org>
George Jones logs in as Jones on his host. His secretary, who logs in
as Secy sends mail for him. Replies to the
mail should go to George.
From: George Jones <Jones@Group>
From: George Jones<Shared@Group.Org>
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.
A.2.4. Committee activity, with one author
George is a member of a committee. He wishes to have any
replies to his message go to all committee members.
From: George Jones <Jones@Host.Net>
Reply_To: The Committee: Jones@Host.Net,
Doe@Somewhere_Else;Note that if George had not included himself in the enumeration of The 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.
A.2.5. Secretary acting as full agent of author
George Jones asks his secretary (Secy@Host) to send a
message for him in his capacity as Group. He wants his secretary to handle
From: George Jones <Group@Host>
From: Sarah Friendly <Secy@Registry>
Sender: Secy_Name <Secy@Registry>
A.3.1. Minimum required
Date: 26 Aug 76 1429 EDT Date: 26 Aug 76 1429 EDT
From: Jones@Registry.Org or From: Jones@Registry.Org
Bcc: To: Smith@Registry.Org
Note that the "Bcc" field may be empty, while the "To" field is required to have at least one address.
A.3.2. Using some of the additional fields
Date: 26 Aug 76 1430 EDT
From: George Jones<Group@Host>
To: "Al Neuman"@Mad_Host,
A.3.3. About as complex as you're going to get
Date : 27 Aug 76 0932 PDT
From : Ken Davis <KDavis@This_Host.This_net>
Subject : Re: The Syntax in the RFC
Sender : KSecy@Other_Host
Reply_To : Sam.Irving@Reg.Organization
To : George Jones <Group@Some_Reg.An_Org>,
cc : Important folk:
Tom Softwood <Balsa@Tree.Root>,
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
In_Reply_To: <some.string@DBM.Group>, George's message
X_Special_action: This is a sample of user_defined field_
names. There could also be a field_name
"Special_action", but its name might later be
. . . . . . . . . ( end of section A) <<Contents | End>>
B. SIMPLE FIELD PARSING
Some mail_reading software systems may wish to perform only minimal processing, ignoring the internal syntax of structured field_bodies and treating them the same as unstructured_field_bodies. Such software will need only to distinguish:
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, space, and control_characters). A field_name MUST be contained on one line. Upper and lower case are not distinguished when comparing field_names.
C. DIFFERENCES FROM RFC #733
The following summarizes the differences between this standard and the one specified in Arpanet Request for Comments #733, "Standard for the Format of ARPA Network Text Messages". The differences are listed in the order of their occurrence in the current specification.
C.1. FIELD DEFINITIONS
C.1.1. FIELD NAMES
These now must be a sequence of printable characters. They may not contain any LWSP_chars.
C.2. LEXICAL TOKENS
The characters period ("."), left_square bracket ("["), and right_square bracket ("]") have been added. For presentation purposes, and when passing a specification to a system that does not conform to this standard, periods are to be contiguous with their surrounding lexical tokens. No linear_white_space is permitted between them. The presence of one LWSP-char between other tokens is still directed.
Atoms may not contain SPACE.
C.2.3. SPECIAL TEXT
ctext and qtext have had backslash ("\") added to the list of prohibited characters.
The lexical tokens domain_literal and dtext have been added.
C.3. MESSAGE SPECIFICATION
The "Return_path:" and "Received:" fields have been specified.
The "From" field must contain machine_usable addresses (addr_spec). Multiple addresses may be specified, but named_lists (groups) may not.
The meta_construct of prefacing field names with the string "Resent-" has been added, to indicate that a message has been forwarded by an intermediate recipient.
A message must contain at least one destination address field. "To" and "CC" are required to contain at least one address.
The field_body is no longer a comma_separated list, although a sequence is still permitted.
The field_body is no longer a comma_separated list, although a sequence is still permitted.
A field has been specified that permits senders to indicate that the body of a message has been encrypted.
Extension fields are prohibited from beginning with the characters "X-".
C.4. DATE AND TIME SPECIFICATION
Fewer optional forms are permitted and the list of three-letter time zones has been shortened.
C.5. ADDRESS SPECIFICATION
The use of quoted_string, and the ":"_atom_":" construct, have been removed. An address now is either a single mailbox reference or is a named list of addresses. The latter indicates a group distribution.
Group lists are now required to to have a name. Group lists may not be nested.
A mailbox specification may indicate a person's name, as before. Such a named list no longer may specify multiple mailboxes and may not be nested.
C.5.4. ROUTE ADDRESSING
Addresses now are taken to be absolute, global specifications, independent of transmission paths. The route construct has been provided, to permit explicit specification of transmission path. RFC #733's use of multiple at_signs ("@") was intended as a general syntax for indicating routing and|or hierarchical addressing. The current standard separates these specifications and only one at_sign is permitted.
The string " at " no longer is used as an address delimiter. Only at_sign ("@") serves the function.
Hierarchical, logical name_domains have been added.
C.6. RESERVED ADDRESS
The local_part "Postmaster" has been reserved, so that users can be guaranteed at least one valid address at a site.
. . . . . . . . . ( end of section c) <<Contents | End>>
. . . . . . . . . ( end of section Annexes) <<Contents | End>>