RFC 984 (rfc984) - Page 2 of 31

PCMAIL: A distributed mail system for personal computers

RFC 984                                                         May 1986
PCMAIL


   either to succeed completely, or fail completely).  A client can be
   abruptly disconnected from the repository without leaving
   inconsistent or damaged mail states.

   Pcmail is a mail system for PCs.  Its design has therefore been
   heavily influenced by several characteristics unique to PCs. First,
   PCs are relatively inexpensive.  This means that people may own more
   than one PC, perhaps putting one in an office and one at home.
   Second, PCs are portable.  Most PCs can be packed up and moved in the
   back seat of an automobile, and a few are truly portable--about the
   size of a briefcase--and battery-powered.  Finally, PCs are
   resource-poor.  A typical PC has a small amount (typically less than
   one megabyte) of main memory and little in the way of mass storage
   (floppy-disk drives that can access perhaps 360 kilobytes of data).

   Because PCs are relatively inexpensive and people may own more than
   one, Pcmail has been designed to allow users multiple access points
   to their mail state.  Each Pcmail user can have several client PCs,
   each of which can access the user's mail by communicating with the
   repository over a network.  The client PCs all maintain local copies
   of the user's global mail state, and synchronize the local and global
   states using DMSP.

   It is possible, even likely, that many PCs will only infrequently be
   connected to a network (and thus be able to communicate with the
   repository).  The Pcmail design therefore allows two modes of
   communication between repository and client. "Interactive mode" is
   used when the client PC is always connected to the network.  Any
   changes to the client's local mail state are immediately also made to
   the repository's global mail state, and any incoming mail is
   immediately transmitted from repository to client.  "Batch mode" is
   used by clients that have infrequent access to the repository.  Users
   manipulate the client's local mail state, queueing the changes as
   "actions".  When next connected to the repository, the actions are
   transmitted, and the client's local mail state is synchronized with
   the repository's global mail state.

   Finally, the Pcmail design minimizes the effect of using a
   resource-poor PC as a client.  Mail messages are split into two
   parts:  a "descriptor" and a "body".  The descriptor is a capsule
   message summary whose length (typically about 100 bytes) is
   independent of the actual message length.  The body is the actual
   message text, including an RFC-822 standard message header. While the
   client may not have enough storage to hold a complete set of
   messages, it can always hold a complete set of descriptors, thus




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