RFC 1056 (rfc1056) - Page 2 of 38
PCMAIL: A distributed mail system for personal computers
Alternative Format: Original Text Document
RFC 1056 PCMAIL June 1988
2. Introduction
Pcmail is a distributed mail system providing mail service to an
arbitrary number of users, each of whom owns one or more
workstations. Pcmail's motivation is to provide very flexible mail
service to a wide variety of different workstations, ranging in power
from small, resource-limited machines like IBM PCs to resource-rich
(where "resources" are primarily processor speed and disk space)
machines like Suns or Microvaxes. It attempts to provide limited
service to resource-limited workstations while still providing full
service to resource-rich machines. It is intended to work well with
machines only infrequently connected to a network as well as machines
permanently connected to a network. It is also designed to offer
diskless workstations full mail service.
The system is divided into two halves. The first consists of a
single entity called the "repository". The repository is a storage
center for incoming mail. Mail for a Pcmail user can arrive
externally from the Internet or internally from other repository
users. The repository also maintains a stable copy of each user's
mail state (this will hereafter be referred to as the user's "global
mail state"). The repository is therefore typically a computer with
a large amount of disk storage.
The second half of Pcmail consists of one or more "clients". Each
Pcmail user may have an arbitrary number of clients, typically
single-user workstations. The clients provide a user with a friendly
means of accessing the user's global mail state over a network. In
order to make the interaction between the repository and a user's
clients more efficient, each client maintains a local copy of its
user's global mail state, called the "local mail state". It is
assumed 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
System 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
message", "print a message", etc.). DMSP also provides special
operations 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
Lambert