Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!cbosgd!ulysses!bellcore!decvax!decwrl!pyramid!pesnta!amd!amdcad!lll-crg!seismo!brl-adm!ron From: ron@brl-adm.UUCP Newsgroups: mod.sources.doc Subject: rfc822 (4 of 5) Message-ID: <725@brl-adm.ARPA> Date: Tue, 20-May-86 00:00:13 EDT Article-I.D.: brl-adm.725 Posted: Tue May 20 00:00:13 1986 Date-Received: Sat, 24-May-86 22:27:20 EDT Distribution: net Organization: Ballistic Research Lab Lines: 580 Approved: RON@BRL.ARPA Standard for ARPA Internet Text Messages Name-domains model a global, logical, hierarchical addressing scheme. The model is logical, in that an address specifica- tion 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 con- stitute name-domains that are independent logically of specific machines. In addition, networks and machines impli- citly 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: person@registry.organization Note that "organization" is a logical entity, separate from any particular communication network. A mechanism for accessing "organization" is universally avail- able. That mechanism, in turn, seeks an instantiation of the registry; its location is not indicated in the address specif- ication. It is assumed that the system which operates under the name "organization" knows how to find a subordinate regis- try. The registry will then use the "person" string to deter- mine where to send the mail specification. The latter, network-oriented case permits simple, direct, attachment-related address specification, such as: user@host.network Once the network is accessed, it is expected that a message will go directly to the host and that the host will resolve August 13, 1982 - 28 - RFC #822 Standard for ARPA Internet Text Messages 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: For the address of the sender, call the left-most sub-domain Level N. In a header address, if all of the sub-domains above (i.e., to the right of) Level N are the same as those of the sender, then they do not have to appear in the specification. Otherwise, the address must be fully qualified. This feature is subject to approval by local sub- domains. Individual sub-domains may require their member systems, which originate mail, to provide full domain specification only. When permitted, abbrevia- tions 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 abbrevi- ated specifications. For example, if a sender's address is: sender@registry-A.registry-1.organization-X and one recipient's address is: recipient@registry-B.registry-1.organization-X and another's is: recipient@registry-C.registry-2.organization-X 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 abbrevi- ated, 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 August 13, 1982 - 29 - RFC #822 Standard for ARPA Internet Text Messages with this requirement. In the case of abbreviated addresses, 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 exam- ple, 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. Note: When passing any portion of an addr-spec onto a process which does not interpret data according to this stan- dard (e.g., mail protocol servers). There must be NO LWSP-chars preceding or following the at-sign or any delimiting period ("."), such as shown in the above examples, and only ONE SPACE between contiguous s. 6.2.3. DOMAIN TERMS A domain-ref must be THE official name of a registry, network, or host. It is a symbolic reference, within a name sub- domain. At times, it is necessary to bypass standard mechan- isms 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 Inter- net specify 32-bit Internet addresses, in four 8-bit fields noted in decimal, as described in Request for Comments #820, "Assigned Numbers." For example: [10.0.3.19] Note: THE USE OF DOMAIN-LITERALS IS STRONGLY DISCOURAGED. It is permitted only as a means of bypassing temporary system limitations, such as name tables which are not complete. The names of "top-level" domains, and the names of domains under in the ARPA Internet, are registered with the Network Information Center, SRI International, Menlo Park, California. 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 August 13, 1982 - 30 - RFC #822 Standard for ARPA Internet Text Messages whatever the receiving mail protocol server allows. For exam- ple, 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 uninter- preted unit. The sequence will be re-assembled, when the address is passed outside of the system such as to a mail pro- tocol service. For example, the address: First.Last@Registry.Org 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: mailbox.sub1.sub2@this-domain 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 stan- dard, the form is legal. Also, some sub-domains have a specification syntax which does not conform to this standard. For example: sub-net.mailbox@sub-domain.domain August 13, 1982 - 31 - RFC #822 Standard for ARPA Internet Text Messages uses a different parsing sequence for local-part than for domain. Note: As a rule, the domain specification should contain fields which are encoded according to the syntax of this standard and which contain generally-standardized information. The local-part specification should con- tain only that portion of the address which deviates from the form or intention of the domain field. 6.2.6. MULTIPLE MAILBOXES 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 construct permits specification of such a list. Recipient mailboxes are speci- fied 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 con- tents of the list be included. In this case, the
serves only as an indication of group distribution and would appear in the form: name:; 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 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 portion of a route-addr is provided for such occa- sions. It specifies the sequence of hosts and/or transmission August 13, 1982 - 32 - RFC #822 Standard for ARPA Internet Text Messages services that are to be traversed. Both domain-refs and domain-literals may be used. Note: The use of source routing is discouraged. Unless the sender has special need of path restriction, the choice of transmission route should be left to the mail tran- sport service. 6.3. RESERVED ADDRESS It often is necessary to send mail to a site, without know- ing any of its valid addresses. For example, there may be mail system dysfunctions, or a user may wish to find out a person's correct address, at that site. This standard specifies a single, reserved mailbox address (local-part) which is to be valid at each site. Mail sent to that address is to be routed to a person responsible for the site's mail system or to a person with responsibility for general site operation. The name of the reserved local-part address is: Postmaster so that "Postmaster@domain" is required to be valid. Note: This reserved local-part must be matched without sensi- tivity to alphabetic case, so that "POSTMASTER", "postmas- ter", and even "poStmASteR" is to be accepted. August 13, 1982 - 33 - RFC #822 Standard for ARPA Internet Text Messages 7. BIBLIOGRAPHY 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 Hand- book", NIC 7104. ANSI. "Representations of Universal Time, Local Time Differen- tials, and United States Time Zone References for Information Interchange," X3.51-1975. American National Standards Insti- tute: New York (1975). Bemer, R.W., "Time and the Computer." In: Interface Age (Feb. 1979). Bennett, C.J. "JNT Mail Protocol". Joint Network Team, Ruther- ford 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," Communica- tions 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, Net- work 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). August 13, 1982 - 34 - RFC #822 Standard for ARPA Internet Text Messages 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 Environ- ment," 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). August 13, 1982 - 35 - RFC #822 Standard for ARPA Internet Text Messages APPENDIX A. EXAMPLES A.1. ADDRESSES A.1.1. Alfred Neuman A.1.2. Neuman@BBN-TENEXA These two "Alfred Neuman" examples have identical seman- tics, as far as the operation of the local host's mail sending (distribution) program (also sometimes called its "mailer") and the remote host's mail protocol server are concerned. In the first example, the "Alfred Neuman" is ignored by the mailer, as "Neuman@BBN-TENEXA" completely specifies the reci- pient. The second example contains no superfluous informa- tion, and, again, "Neuman@BBN-TENEXA" is the intended reci- pient. Note: When the message crosses name-domain boundaries, then these specifications must be changed, so as to indicate the remainder of the hierarchy, starting with the top level. A.1.3. "George, Ted" 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, because "Shared@Group.Arpanet" completely specifies the destination mailbox. A.1.4. Wilt . (the Stilt) Chamberlain@NBA.US The "(the Stilt)" is a comment, which is NOT included in the destination mailbox address handed to the originating system's mailer. The local-part of the address is the string "Wilt.Chamberlain", with NO space between the first and second words. A.1.5. Address Lists Gourmets: Pompous Person , Childs@WGBH.Boston, Galloping Gourmet@ ANT.Down-Under (Australian National Television), Cheapie@Discount-Liquors;, Cruisers: Port@Portugal, Jones@SEA;, Another@Somewhere.SomeOrg August 13, 1982 - 36 - RFC #822 Standard for ARPA Internet Text Messages This group list example points out the use of comments and the mixing of addresses and groups. A.2. ORIGINATOR ITEMS A.2.1. Author-sent George Jones logs into his host as "Jones". He sends mail himself. From: Jones@Group.Org or From: George Jones A.2.2. Secretary-sent George Jones logs in as Jones on his host. His secre- tary, who logs in as Secy sends mail for him. Replies to the mail should go to George. From: George Jones Sender: Secy@Other-Group A.2.3. Secretary-sent, for user of shared directory George Jones' secretary sends mail for George. Replies should go to George. From: George Jones Sender: Secy@Other-Group 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 Sender: Jones@Host Reply-To: The Committee: Jones@Host.Net, Smith@Other.Org, Doe@Somewhere-Else; Note that if George had not included himself in the August 13, 1982 - 37 - RFC #822