RFC 993 (rfc993) - Page 2 of 28

PCMAIL: A distributed mail system for personal computers

RFC 993                                                    December 1986


   user's global mail state, called the "local mail state".  It is as-
   sumed that clients, possibly being small personal computers, may not
   always have access to a network (and therefore to the global mail
   state in the repository).  This means that the local and global mail
   states may not be identical all the time, making synchronization
   between local and global mail states necessary.

   Clients communicate with the repository via the Distributed Mail Sys-
   tem Protocol (DMSP); the specification for this protocol appears in
   appendix A. The repository is therefore a DMSP server in addition to
   a mail end-site and storage facility.  DMSP provides a complete set
   of mail manipulation operations ("send a message", "delete a mes-
   sage", "print a message", etc.).  DMSP also provides special opera-
   tions to allow easy synchronization between a user's global mail
   state and his clients' local mail states.  Particular attention has
   been paid to the way in which DMSP operations act on a user's mail
   state.  All DMSP operations are failure-atomic (that is, they are
   guaranteed either to succeed completely, or leave the user's mail
   state unchanged ).  A client can be abruptly disconnected from the
   repository without leaving inconsistent or damaged mail states.

   Pcmail's design has been directed by the characteristics of currently
   available workstations.  Some workstations are fairly portable, and
   can be packed up and moved in the back seat of an automobile.  A few
   are truly portable--about the size of a briefcase--and battery-
   powered.  Some workstations have constant access to a high-speed
   local-area network; pcmail should allow for "on-line" mail delivery
   for these machines while at the same time providing "batch" mail
   delivery for other workstations that are not always connected to a
   network.  Portable and semi-portable workstations tend to be
   resource-poor.  A typical IBM 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).  Pcmail must be able to provide machines like this with ade-
   quate mail service without hampering its performance on more
   resource-rich workstations. Finally, all workstations have some com-
   mon characteristics that Pcmail should take advantage of.  For in-
   stance, workstations are fairly inexpensive compared to the various
   time-shared systems that most people use for mail service.  This
   means that people may own more than one workstation, perhaps putting
   a Microvax in an office and an IBM PC at home.

   Pcmail's design reflects the differing characteristics of the various
   workstations.  Since one person can own several workstations, Pcmail
   allows users multiple access points to their mail state.  Each Pcmail
   user can have several client workstations, each of which can access
   the user's mail by communicating with the repository over a network.
   The clients all maintain local copies of the user's global mail
   state, and synchronize the local and global states using DMSP.

   It is also possible that some workstations will only infrequently be



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