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rfc:rfc754

RFC 754 J. Postel

                                                                   ISI
                                                          6 April 1979
                 Out-of-Net Host Addresses for Mail

There is now interest in sustantially extending the scope of the computer mail system used in the ARPANET to allow communication of voice, fax, graphics, as well as text information between users in different networks as wells as within the ARPANET.

The discussion of a transition from the current ARPANET sndmsg environment and mechanisms to a more general internet environment and richer mechanisms must consider techniques for continued activity during the transition. In addition, there is a current need for a mechanism to support the interaction of the several already existing NSW-like message environments with the ARPANET message environment.

This memo discusses some possible alternatives for computer mail addressing for hosts outside the ARPANET in the short term. This memo is hopelessly Tenex oriented in its descriptions and examples.

It helps to keep a few goals in mind while considering the alternative solutions:

Goals:

 1) Minimum Change to Existing Software.
 2) Maximum User Acceptance.
 3) Maximum Compatibility with the future Internet Message
 Environment.
 4) Minimum Special Transition Software.

These goals are to some degree incompatible, so the evaluation should be expected to involve a trade off.

At this point, it would be good to have a model of the current situation and mechanisms of the ARPANET message environment. It is assumed the reader understands it well enough to dispense with a long description of how a message gets from A to B. The important thing is to note the types of players in the picture. There are:

 message composition (or sending) programs (e.g., Hermes, SNDMSG), in
 general there are several message composition programs for each type
 of operating system or host in the network,

Postel [page 1]

RFC 754 6 April 1979 Out-of-Net Host Addresses for Mail

 mailers,
 mail servers (i.e., FTP servers) that receive the mail coming into at
 host and deposit it in mailboxes,
 message processing (or reading) programs (e.g., Hermes, MSG, RD), in
 general there are several message processing programs for each type
 of operating system or host in the network,  and note that the more
 developed mail are both reading and sending programs.

Messages are transmitted as a character string to an address which is specified "outside" the message. The destination host ("YYY") is specified to the sending (or user) FTP as the argument of the "open connection" command, and the destination user ("XXX") is specified to the receiving (or server) FTP as the argument of the "MAIL" (or "MLFL") command. In Tenex, when mail is queued this outside information is saved in the file name ("[—].XXX@YYY").

The proposed solutions are briefly characterized.

Proposed Solutions:

 This first pass at describing the solutions is rather brief and
 intended to set the scene for a subsequent discussion based on
 examples.
 A) SINGLE MAILBOX
    This solution suggests that all mail for another network be routed
    to a single mailbox on a forwarding host on the ARPANET.  The FTP
    server would naturally put all the mail for this mailbox into a
    single file to be examined by a routing deamon process.  The
    routing deamon process would use information in new header lines
    to determine the actual destination.
    Format:
       Outside:  [---].NSW-MAIL@FWDR
       Inside:   To:       NSW-MAIL@FWDR
                 From:     Sam@ISIB
                 NSW-User: Joe

Postel [page 2]

RFC 754 6 April 1979 Out-of-Net Host Addresses for Mail

 B) GLOBAL NAMES INSIDE
    This proposal suggests that all mail for users in another network
    be sent to a single mailbox on a forwarding host.  The FTP server
    would naturally put all the mail for this mailbox into a single
    file to be examined by a routing deamon process.  The routing
    deamon process would use information in existing header lines to
    determine the actual destination.
    Format:
       Outside: [---].NSW-MAIL@FWDR
       Inside:  To:   Joe@NSW
                From: Sam@ISIB
 C) GLOBAL NAMES OUTSIDE
    This proposal suggests that mail for users in another network be
    sent to distinct per user mailbox names on a forwarding host.  The
    FTP server would somehow put all the mail for these mailboxes into
    a single file to be examined by a routing deamon process.  The
    routing deamon process would use information in existing header
    lines to determine the actual destination.
    Format:
       Outside: [---].Joe@FWDR or [---].Joe@NSW
       Inside:  To:   Joe@NSW
                From: Sam@ISIB
 D) STRUCTURED NAMES
    This proposal suggests that mail for users in another network be
    sent to distinct per user mailbox names on a forwarding host,
    however, these mailbox names would have a common "network" part
    and a unique "user" part.  By recognizing the common part the FTP
    server would put the mail and the mailbox name into a single file
    to be examined by a routing deamon process.  The routing deamon
    process would use mailbox name information to determine the actual
    destination.

Postel [page 3]

RFC 754 6 April 1979 Out-of-Net Host Addresses for Mail

    Format:
       Outside:  [---].NSW-Joe@FWDR
       Inside:  To:   NSW-Joe@FWDR
                From: Sam@ISIB

Before further examination of the advantages and disadvantages of these proposals, it would be well to have some more detailed criteria in mind to help expose the degree to which the goals are met.

Criteria:

 1) What changes are needed?
 2) How many instances of the change need to be implemented?
 3) What information does the routing deamon use?
 4) How does the "answer" command work?
 5) How is the name space used?
 It is particularly instructive to work through examples with a
 mixture of mailbox destinations in the ARPANET and other networks in
 each of the "To:" and "CC:" fields and to see what happens when one
 wants to send an answer to all, just the "To:", or just the "CC:", or
 just the "From:" or "Sender:" mailboxes.

Solutions Reconsidered:

 It is easier to talk about these things in terms of examples.  In the
 following "NSW" is an example of a network name.  "FWDR" is a host
 name, or nickname for the forwarding host.  Also note that for all of
 these solutions it is assumed that host tables can have alternate or
 nicknames for hosts, e.g., FWDR could map to 86 while ISI also maps
 to 86, although this is not essential.
 In addition, all these solutions provide a single forwarding point
 from the ARPANET into the destination net.
 All forwarded messages are handled by a routing deamon which lives in
 the FWDR host.
 Also note that the information shown as the "outside" information is
 the Tenex representation.  The key thing is the mailbox argument
 value that is passed to the FTP server is the one in the string

Postel [page 4]

RFC 754 6 April 1979 Out-of-Net Host Addresses for Mail

 "[---].XXX@YYY", not anything from the header.  Only the string "XXX"
 is passed to the FTP server.
 A) SINGLE MAILBOX
    Example:
       Outside:  [---].NSW-MAIL@FWDR
       Inside:   To:       NSW-MAIL@FWDR,Bill@ISIA
                 CC:       Jeff@ISIB
                 From:     Joe@ISIB
                 NSW-User-To: SAM,Fred
                 NSW-User-CC: Bob,Mike
       or
       Outside:  [---].NSW-MAIL@FWDR
       Inside:   To:       NSW-MAIL@FWDR,Bill@ISIA
                 CC:       Jeff@ISIB
                 From:     NSW-MAIL@FWDR
                 NSW-User-To: SAM,Fred
                 NSW-User-CC: Bob,Mike
                 NSW-User-From: Paul
    Every mail composition program has to change to make it easy for
    users to put the "NSW-User:" line in the header.  Every mail
    reading program has to change to notice and make use of this line.
    In an "answer" command the mail processing program has to know to
    copy this line into the answer message.  The deamon has to examine
    the inside message header to find the "NSW-User:" line and forward
    the message to the users listed there.  If there is a message that
    has both NSW and ARPANET mailboxes in both the "To:" and "CC:"
    lines, then it seems there must be both a "NSW-Users-To:" and a
    "NSW-Users-CC:" lines if it is to be possible to send an answer to
    just the users in the "To:" lines.  If there is another network,
    e.g. PRNET, then another set of header lines must be introduced,
    e.g. PRNET-USER-To: etc., that is up to four new lines per network
    (To, CC, From, Sender).
    This solution has the advantage of saving some transmissions:
    when several of the destination mailboxes are in NSW, the sending
    program sends just one copy to the FWDR and routing deamon, the
    routing deamon sends copies to all NSW users it finds.  If this is
    not done, the deamon would have difficulty avoiding sending
    multiple copies to each destination user.

Postel [page 5]

RFC 754 6 April 1979 Out-of-Net Host Addresses for Mail

    A problem arises about acknowledgements of mail receipt.  First
    the normal ARPANET message delivery mechanisms will say the mail
    is delivered when the FTP server puts the mail in the file for the
    routing deamon to examine.  Second if the routing deamon discovers
    an message is to be forwarded to a nonexistent user, care must be
    used to notify the original sender unambiguously.
    Changes:
       all composition programs
 B) GLOBAL NAMES INSIDE
    Example:
       Outside:  [---].NSW-MAIL@FWDR
       Inside:   To:       Joe@NSW, Bill@ISIA, Fred@NSW
                 CC:       Mike@NSW, Paul@NSW, John@ISIB
                 From:     Sam@ISIB
    Every mail composition program has to know that NSW is a very
    special host name, for which it uses a different mailbox argument
    and sends to the FWDR host.  The FTP server naturally puts all the
    NSW mail into a single mailbox file which the routing deamon
    examines.  The "answer" command works fine.  The routing deamon
    has to look at the inside header to determine where to forward the
    messages.  It has to check the "To:" and "CC:" lines.
    The sending programs must also send just one copy to the FWDR and
    routing deamon, the routing deamon will send copies to all NSW
    users it finds.  If this is not done, the deamon would have
    difficulty avoiding sending multiple copies to each destination
    user.  This is an advantage in terms of number of transmissions.
    A problem arises about acknowledgements of mail receipt.  First
    the normal ARPANET message delivery mechanisms will say the mail
    is delivered when the FTP server puts the mail in the file for the
    routing deamon to examine.  Second if the routing deamon discovers
    an message is to be forwarded to a nonexistent user, care must be
    used to notify the original sender unambiguously.
    Changes:
       all sending programs

Postel [page 6]

RFC 754 6 April 1979 Out-of-Net Host Addresses for Mail

 C) GLOBAL NAMES OUTSIDE
    Example:
       Outside:  [---].Joe@NSW
       Inside:   To:       Joe@NSW, Bill@ISIA, Fred@NSW
                 CC:       Mike@NSW, Paul@NSW, John@ISIB
                 From:     Sam@ISIB
    No changes to mail composition or processing programs are needed.
    The FTP server has to put all the NSW users mail into a single
    mailbox file which the routing deamon examines.  The cheapest way
    to do this is to put all the names of the NSW users in the ARPANET
    user forwarding file with the same destination ARPANET mailbox.
    This means the local users of the FWDR host and the users in the
    destination networks share the name space for user names.  The
    routing deamon has to look at the inside header to determine where
    to forward the messages.  It has to check the "To:" and "CC:"
    lines.
    This appears to be the solution with the minimum change to
    existing software.  The "answer" command works fine.
    There is a problem with the name space, for example, if ISIA
    serves as FWDR host, then Fred@ISI and Fred@NSW cannot co-exist.
    Further, there is the database update problem.  Every time a new
    user is added to NSW or any of the hosts in any of the nets that
    the FWDR host serves the forwarding file at the FWDR host has to
    be updated.  The names added have to be unique so all user names
    assigned in NSW and all the hosts on all the networks served by
    the same FWDR host have to be oked by the "forwarding file data
    base administrator" before they can actually be used.  Also note
    that Fred@NSW and Fred@PRNET cannot be routed through the same
    FWDR host.
    This doesn't work too well, if the sending programs are not
    changed they will send one copy of this message for each NSW user
    and all these copies will end up in the file to be examined by the
    routing deamon.  If the FTP server code is not changed the outside
    information will be lost and the routing deamon will have no idea
    which NSW user this copy is for.  To do the job right with the
    information available the routing deamon would have to keep a
    substantial record about each message it handled checking to see
    if it received for, and send a copy to, each intended destination
    user.

Postel [page 7]

RFC 754 6 April 1979 Out-of-Net Host Addresses for Mail

    A problem arises about acknowledgements of mail receipt.  First
    the normal ARPANET message delivery mechanisms will say the mail
    is delivered when the FTP server puts the mail in the file for the
    routing deamon to examine.  Second if the routing deamon discovers
    an message is to be forwarded to a nonexistent user, care must be
    used to notify the original sender unambiguously.
    Changes:
       ARPANET user forwarding file at FWDR host
 D) STRUCTURED NAMES
    Example:
       Outside:  [---].NSW-Joe@NSW
       Inside:   To:       NSW-Joe@NSW, Bill@ISIA, NSW-Fred@NSW
                 CC:       NSW-Mike@NSW, NSW-Paul@NSW, John@ISIB
                 From:     Sam@ISIB
    No changes to mail composition or processing programs are needed.
    The FTP server has to put all the NSW-x users mail into a single
    file which the routing deamon examines.  The FTP server can do
    this on the recognition of the "NSW-" prefix without knowing all
    the legal individual users.  In addition the FTP server puts the
    mailbox argument into the file with the message.  This is
    necessary to avoid the loss of the "outside" information.  The
    routing deamon can then look at the mailbox argument to determine
    where to forward the messages.  It need not look at the inside of
    the message at all.  The "answer" command works fine.
    A problem arises about acknowledgements of mail receipt.  First
    the normal ARPANET message delivery mechanisms will say the mail
    is delivered when the FTP server puts the mail in the file for the
    routing deamon to examine.  However, if the routing deamon
    discovers an message is to be forwarded to a nonexistent user, the
    deamon can easily tell the original sender the exact destination
    user that is unreachable.
    Changes:
       FTP server at FWDR host

Postel [page 8]

RFC 754 6 April 1979 Out-of-Net Host Addresses for Mail

Summary:

                               A         B        C        D
                             Single    Global   Global   Structured
                             Mailbox   Names    Names    Names
                                       Inside   Outside
 Criteria:
    1) What changes?         Composer  Composer None      FTP server
    2) How many?             100       100      0         1
    3) Routing information?  New       Old      Old       Old
                             Inside    Inside   Inside    Outside
    4) "Answer" command?     Changes   Same     Same      Same
    5) ARPANET name space    1 per     1 per    1 per     1 per
       use?                  FWDR      FWDR     user      user
 Goals:
    1) Software Change       Bad       Bad      Good      Good
    2) User Acceptance       Bad       Good     Good      Poor
    3) Future Compatibility  Bad       Poor     Poor      Fair
    4) Transition Software   Fair      Good     Bad       Good
 Conclusions:
    Solution D is recommended.
    Only solution D is based on the use of strictly "outside"
    information.  Please note that the existing ARPANET message
    DELIVERY system is based strictly on the use of "outside"
    information only.  Also note that the problems that keep coming up
    in ARPANET message processing & composition programs have to do
    with the different possibilities for syntax (and semanitcs) of the
    "inside" information.  This is a major advantage of solution D.

Postel [page 9]

RFC 754 6 April 1979 Out-of-Net Host Addresses for Mail

    Please note that the syntax NET-USER@FWDR in the examples is not
    the only form that could be used.  Any of the following (or even
    others) would be fine:
       Net-User@FWDR       User-Net@FWDR
       Net/User@FWDR       User/Net@FWDR
       Net.User@FWDR       User.Net@FWDR
       Net.and.User@FWDR   User.on.Net@FWDR

Postel [page 10]

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