GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc771

Network Working Group V. Cerf (ARPA) Request for Comments: 771 J. Postel (ISI)

                                                        September 1980
                        MAIL TRANSITION PLAN

PREFACE

 This is a draft memo and comments are requested.

INTRODUCTION

 The principal aim of the mail service transition plan is to provide
 orderly support for computer mail service during the period of
 transition from the old ARPANET protocols to the new Internet
 protocols.
 This plan covers only the transition from the current text computer
 mail in the ARPANET environment to text computer mail in an Internet
 environment.  This plan does not address a second transition from
 text only mail to multimedia mail [10,11].
 The goal is to provide equivalent or better service in the new
 Internet environment as was available in the ARPANET environment.
 During the interim period, when both protocol environments are in
 use, the goal is to minimize the impact on users and existing
 software, yet to permit the maximum mail exchange connectivity.
 It is assumed that the user is familiar with both the ARPANET and
 Internet protocol environments [1-8].  The Internet protocols are
 designed to be used in a diverse collection of networks including the
 ARPANET, Packet Radio nets, Satellite nets, and local nets (e.g.,
 Ethernets, Ring nets); while the ARPANET protocol are, of course,
 limited to the ARPANET.
 The Internet protocol environment specifies TCP as the host-to-host
 transport protocol.  The ARPANET protocol environment specifies NCP
 as the host-to-host transport protocol.  Both TCP and NCP provide
 connection type process-to-process communication.  The problem in the
 transition is to bridge these two different interprocess
 communication systems.
 The objective of this plan is to specify the means by which the
 ARPANET computer mail services may be extended into the Internet
 system without disruptive changes for the users during the
 transition.
                                 1

September 1980 RFC 771 Mail Transition Plan

MODEL OF MAIL SERVICE

 The model of the computer mail system taken here separates the mail
 composition and reading functions from the mail transport functions.
 In the following, the discussion will be hoplessly TOPS20-oriented.
 We appologize to users of other systems, but  we feel it is better to
 discuss examples we know than to attempt to be abstract.
 In the ARPANET mail service, composition and reading is done with
 user programs such as HERMES, MSG, MM, etc., while mail transmission
 is done by system programs such as MAILER (sending) and FTPSRV
 (receiving).
 One element of the ARPANET mail service is the assumption that every
 source of mail can have a direct interprocess communication
 connection (via the NCPs) to every destination for mail.  (There are
 some cases where special handling and forwarding of mail violates
 this assumption.)
 Mailbox names are of the form "MAILBOX@HOST", and it is assumed that
 MAILBOX is a destination mailbox on that host.
 The messages are actually transmitted according to the provisions of
 the File Transfer Protocol.  Mail may be transimitted via either the
 control connection (MAIL command), or via a data connection (MLFL
 command).  In either case, the argument specifies only the mailbox
 since the destination host is assumed to be the host receiving the
 transmission.
    For example:  messages sent from Postel at USC-ISIF to Cerf at
    USC-ISIA would arrive at ISIA with the argument "Cerf" but no
    indication of the host.

COMPOUND AND ALTERNATE NAMES

 Mailboxes are of the form "mailbox@host" where mailbox is usually a
 name like "Postel" and host is a host identifier like "USC-ISIF".  In
 some cases it will be useful to allow the host to be a compound name
 such as:
    USC-ISIA
    ARPANET-ISIA
    SATNET-NDRE
    PPSN-RSRE
    HOST1.SRINET
    LSCNET/MAILROOM
                                 2

RFC 771 September 1980

                                                  Mail Transition Plan
 or even the name of an organization:
    BBN
    ARPA
    MIT
    SRI
 The only restriction is that "@" not appear in either the "mailbox"
 or the "host" strings in the destination address.
 To actually send the message the mailer program must convert the host
 string into the physical address to which to transmit the message.
 This name-to-address conversion is typically done by looking the name
 up in a table and finding the physical address in another field of
 that table entry.  This means that all the compound and organization
 names (and any other alternate names or synonyms) must also be in the
 host table.

HIDDEN HOSTS

 Sometimes the mailbox part of the destination address is a compound
 name and is used to mark a set of mailboxes which are not really on
 the host at all, but rather on another host which is connected to
 this host in a non-standard way.
 It is important to users of computer mail that replies to messages
 may be easily composed with automatic assistance from the mail
 processing programs.  To preserve this capability it is important
 that a host understand the mailbox part of every address in every
 message it sends if the host part of the address is itself.
 That is, for every message, in every header field, in every address
 "m@h", host h must understand all values of m.  Thus when a host
 prepares a message it should check all the addresses that appear in
 the header and for any address whose host part is this host the
 mailbox part should be verified.
                                 3

September 1980 RFC 771 Mail Transition Plan

THE TRANSITION PLAN

 The basic ground rules for the transition are:
    1.  ARPANET mailbox names must continue to work correctly.
    2.  No changes should be required to mail editor software which
    parses message headers to compose replies and the like.
    Specifically,  non-ARPANET mailbox designators must be
    accommodated without change to the parsing and checking mechanisms
    of mail processing programs.
    3.  Automatic forwarding of messages between NCP and TCP
    environments without user (or operator) intervention.
 For the communication of messages between NCP and TCP hosts a mail
 relay service will be provided on a few hosts that implement both TCP
 and NCP.  These will be "well known" in the same sense that sockets
 or ports for contacting Telnet or FTP servers are well known.
 To make use of these relay servers changes will be made to the mailer
 programs.  The mailer program will be responsible for determining if
 the destination address of the message is directly reachable via the
 interprocess communication system it has available (TCP or NCP or
 both), or if the mail must be relayed.  If the mail must be relayed,
 the mailer must choose a relay server and transmit the message to it.
 The basis for the decision the mailer must make is an expanded host
 name table.  There will be a table which translates host names to
 physical addresses.  The physical addresses in this table will be the
 32-bit Internet addresses. (This makes sense for even NCP-only hosts,
 since after 1 January 1981 even they must use 96-bit leader format
 which requires 24-bit ARPANET physical addresses).  Each entry in
 this table will also have some flag bits.
 The flag bits will include information to indicate if the host in
 this entry is (1) a  NCP host with "old tables", (2) a NCP host with
 "new tables", (3) a TCP host, or (4) some other kind of host.  All
 TCP hosts are assumed to have "new tables".  "Old tables" are those
 without these flag bits, while "new tables" do have these flags.
 A separate table may be useful to list the addresses of the hosts
 with relay servers.
                                 4

RFC 771 September 1980

                                                  Mail Transition Plan
 When a message is sent to a relay server, the control information (in
 the argument of the mail transfer command) must be augmented to
 include the destination host identifier.
 The relay server may accept messages to be relayed without knowing
 that destination mailbox is actually reachable.  This means that it
 may later discover that the destination mailbox does not exist (or
 some other condition prevents mail delivery).  To be able to report
 the error to the originating user, the mailbox (mailbox@host) of the
 originating user must be included in the argument of the mail
 transfer command.  If the argument does not contain the address of
 the originating user no error response is attempted.  The error
 report, which is itself a message, does not carry an originator
 address in the command argument to avoid the possibility of a endless
 chain of error reports (however, an originator address does appear
 the header).
 Since the originating host will act as if the mail was successfully
 delivered when it is accepted by the relay server, it deletes any
 back up copies of the message it was keeping in case of errors.  For
 this reason, the relay server must include the complete message in
 any error report it sends to the originator.  The relay server should
 parse the addresses in the argument before accepting a message.  If
 it does not understand how deliver locally, or both relay and reply
 (if the originating address is present) to the message, it should not
 accept it.
 There are enough differences in the transmission procedure that the
 relay server will use a distinct mail transfer protocol, separate
 from the file transfer protocol.

MAIL TRANSFER PROTOCOL

 The mail trasfer protocol to be used by the relay server and all TCP
 hosts is documented in reference [9].

CONNECTIVITY

 There are nine cases of mail exchange, the three by three matrix of
 (1) old-table NCP hosts, (2) new-table NCP hosts, (3) TCP hosts.
 There are also two transfer mechanisms:  file transfer and mail
 transfer.  The diagonal is easy, each type of host can exchange mail
 with other hosts of its type.  The other cases are more subtle.
                                 5

September 1980 RFC 771 Mail Transition Plan

 An old-table NCP host is assumed to have a table with 32-bit physical
 addresses, but no flag bits.  It has NCP and file transfer.  It does
 not have the separate mail transfer protocol.
 An new-table NCP host is assumed to have a table with 32-bit physical
 addresses, and the flag bits.  It has NCP and file transfer.  It also
 has the new separate mail transfer.
 An TCP host is assumed to have a table with 32-bit physical
 addresses, and the flag bits.  It has the new separate mail transfer.
 It probably has a file transfer, but does not use it for mail.
 1. Old-table NCP to Old-table NCP
    This transfer is direct and uses the old mechanisms -- NCP and
    file transfer.
 2. New-table NCP to Old-table NCP
    This transfer is direct and uses the old mechanisms -- NCP and
    file transfer.
 3. TCP to Old-table NCP
    This transfer must use a relay server.  The first transfer (from
    the TCP host to the relay server) is via TCP and the mail transfer
    protocol.  The second transfer (from the relay server to the
    old-table NCP) is via NCP and file transfer protocol.
 4. Old-table NCP to New-table NCP
    This transfer is direct and uses the old mechanisms -- NCP and
    file transfer.
 5. New-table NCP to New-table NCP
    This transfer is done with the NCP and the mail transfer protocol,
    that is, using the old interprocess communication system and the
    new mail transmission scheme.
 6. TCP to New-table NCP
    This transfer must use a relay server.  The first transfer (from
    the TCP host to the relay server) is via TCP and the mail transfer
    protocol.  The second transfer (from the relay server to the
    new-table NCP) is via NCP and mail transfer protocol.
                                 6

RFC 771 September 1980

                                                  Mail Transition Plan
 7. Old-table NCP to TCP
    This transfer must use a special relay server.  The first transfer
    (from the old-table NCP to the relay server) is via NCP and the
    file transfer protocol.  The second transfer (from the relay
    server to the TCP host) is via TCP and mail transfer protocol.
    This relay server must be special because the messages coming from
    the old-table NCP host will not have the destination host
    information in the command argument.  This relay server must have
    a list of registered TCP user mailboxes and their associated TCP
    host identifiers.  Since such a registry could be potentially
    large and frequently changing (and will grow as more TCP hosts
    come into existence) it will be necessary to limit the mailboxes
    on the registry.
 8. New-table NCP to TCP
    This transfer must use a relay server.  The first transfer (from
    the new-table NCP to the relay server) is via NCP and the mail
    transfer protocol.  The second transfer (from the relay server to
    the TCP host) is via TCP and mail transfer protocol.
 9. TCP to TCP
    This transfer is direct and uses the new mechanisms -- TCP and the
    mail transfer protocol.
 In general, whenever possible the new procedures are to be used.

MULTIPLE RECIPIENTS

 A substantial portion of the mail sent is addressed to multiple
 recipients.  It would substantially cut the transmission and
 processing costs if such multiple recipient mail were transfered
 using the multiple recipient technique available for use in both the
 old file transfer protocol [12] and new mail transfer protocol [9].
 The relay servers will attempt to use a multiple recipient commands
 whenever applicable on transmitting messages, and will accept such
 commands when revceiving messages.
                                 7

September 1980 RFC 771 Mail Transition Plan

COMPOSITION AND READING PROGRAMS

 The impact on the mail composition and reading programs is minimal.
 If these programs use a table to recognize, complete, or verify host
 identifiers, then they must be modified to use the new table.
 To assist the user in replying to messages it will be important that
 all addresses in the header fields (TO:, CC:, etc.) be complete with
 both the mailbox and host parts.  In some cases this has not
 previously been necessary since the addresses without host parts
 could be assumed to be local to the originating host, and the sending
 host was recorded by the receiving host.  When the messages were sent
 directly the originating host was the sending host, but when messages
 are relayed the originating host will not be the host sending the
 mail to the destination host.
                                 8

RFC 771 September 1980

                                                  Mail Transition Plan

REFERENCES

 [1]     Cerf, V., "The Catenet Model for Internetworking," IEN 48,
         DARPA/IPTO, July 1978.
 [2]     Postel, J., "Internet Protocol," RFC 760, USC/Information
         Sciences Institute, NTIS ADA079730, January 1980.
 [3]     Postel, J., "Transmission Control Protocol," RFC 761,
         USC/Information Sciences Institute, NTIS ADA082609,
         January 1980.
 [4]     Postel, J., "Telnet Protocol Specification," RFC 764,
         USC/Information Sciences Institute, June 1980.
 [4]     Postel, J., "File Transfer Protocol," RFC 765,
         USC/Information Sciences Institute, June 1980.
 [5]     Postel, J., "Assigned Numbers," USC/Information Sciences
         Institute, RFC 762, January 1980.
 [6]     Postel, J., "Internet Protocol Handbook," USC/Information
         Sciences Institute, RFC 766, July 1980.
 [7]     Feinler, E. and, J. Postel, "ARPANET Protocol Handbook,"
         NIC 7104, Network Information Center, SRI International,
         January 1978.
 [8]     Crocker, D., J. Vittal, K. Pogran, and, D. Henderson,
         "Standards for the Format of ARPA Network Text Messages,"
         RFC 733 7104, Network Information Center, SRI International,
         November 1977.
 [9]     Sluizer, S. and, J. Postel, "Mail Transfer Protocol,"
         USC/Information Sciences Institute, RFC rrr, September 1980.
 [10]    Postel, J., "Internet Message Protocol," USC/Information
         Sciences Institute, RFC 759, August 1980.
 [11]    Postel, J., "A Structured Format for Transmission of
         Multi-Media Documents," USC/Information Sciences Institute,
         RFC 767, August 1980.
 [12]    Harrenstien, K., "FTP Extension: XRSQ/XRCP,"
         SRI International, RFC 743, December 1977.
                                 9
/data/webs/external/dokuwiki/data/pages/rfc/rfc771.txt · Last modified: 1992/10/15 21:56 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki