RFC 1176 (rfc1176) - Page 2 of 30


Interactive Mail Access Protocol: Version 2



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RFC 1176                         IMAP2                       August 1990


System Model and Philosophy

   Electronic mail is a primary means of communication for the widely
   spread Internet community.  The advent of distributed personal
   computers and workstations has forced a significant rethinking of the
   mechanisms employed to manage electronic mail.  With mainframes, each
   user tends to receive and process mail at the computer he uses most
   of the time, his "primary host".  The first inclination of many users
   when an independent workstation is placed in front of them is to
   begin receiving mail at the workstation, and many vendors have
   implemented facilities to do this.  However, this approach has
   several disadvantages:

      (1) Personal computers and many workstations have a software
      design that gives full control of all aspects of the system to the
      user at the console.  As a result, background tasks such as
      receiving mail may not run for long periods of time; either
      because the user is asking to use all the machine's resources, or
      because the user has (perhaps accidentally) manipulated the
      environment in such a way that it prevents mail reception.  In
      many personal computers, the operating system is single-tasking
      and this is the only mode of operation.  Any of these conditions
      could lead to repeated failed delivery attempts by outside agents.

      (2) The hardware failure of a single machine can keep its user
      "off the air" for a considerable time, since repair of individual
      units may be delayed.  Given the growing number of personal
      computers and workstations spread throughout office environments,
      quick repair of such systems is not assured.  On the other hand, a
      central mainframe is generally repaired soon after failure.

      (3) Personal computers and workstations are often not backed up
      with as much diligence as a central mainframe, if at all.

      (4) It is more difficult to keep track of mailing addresses when
      each person is associated with a distinct machine.  Consider the
      difficulty in keeping track of many postal addresses or phone
      numbers, particularly if there was no single address or phone
      number for an organization through which you could reach any
      person in that organization.  Traditionally, electronic mail on
      the ARPANET involved remembering a name and one of several "hosts"
      (machines) whose name reflected the organization in which the
      individual worked.  This was suitable at a time when most
      organizations had only one central host.  It is less satisfactory
      today unless the concept of a host is changed to refer to an
      organizational entity and not a particular machine.

      (5) It is difficult to keep a multitude of heterogeneous machines



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