RFC 1176 (rfc1176) - Page 2 of 30
Interactive Mail Access Protocol: Version 2
Alternative Format: Original Text Document
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
Crispin