PCMAIL: A distributed mail system for personal computers
RFC 1056

Document Type RFC - Informational (June 1988; No errata)
Obsoletes RFC 993
Last updated 2013-03-02
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Network Working Group                                         M. Lambert
Request for Comments: 1056                                           MIT
Obsoletes: RFC-993                                             June 1988

        PCMAIL: A Distributed Mail System for Personal Computers

                           Table of Contents

   1. Status of this Document                                      1
   2. Introduction                                                 2
   3. Repository architecture                                      4
        3.1. Management of user mail state                         5
        3.2. Repository-to-RFC-822 name translation                7
   4. Communication between repository and client: DMSP            8
        4.1. DMSP commands                                         8
        4.2. DMSP responses                                        8
        4.3. DMSP sessions                                        11
        4.4. General operations                                   11
        4.5. User operations                                      12
        4.6. Client operations                                    13
        4.7. Mailbox operations                                   14
        4.8. Address operations                                   15
        4.9. Subscription operations                              15
        4.10. Message operations                                  16
   5. Client Architecture                                         18
        5.1. Multiple clients                                     18
        5.2. Synchronization                                      18
        5.3. Batch operation versus interactive operation         20
        5.4. Message summaries                                    20
   6. Typical interactive-style client-repository interaction     21
   7. A current Pcmail implementation                             25
        7.1. IBM PC client code                                   25
        7.2. UNIX client code                                     26
        7.3. Repository code                                      26
   8. Conclusions                                                 26
   I. DMSP Protocol Specification                                 28
   II. Operations by name                                         37
   III. Responses by number                                       38

1. Status of this Memo

   This RFC is a discussion of the Pcmail workstation based distributed
   mail system.  It is identical to the discussion in RFC-993, save that
   a new, much simpler mail transport protocol is described.  The new
   transport protocol is the result of continued research into ease of
   protocol implementation and use issues.  Distribution of this memo is

Lambert                                                         [Page 1]
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
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