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Network Working Group                                         M. LambertRequest for Comments: 1056                                           MITObsoletes:RFC-993                                             June 1988PCMAIL: 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                                       381. Status of this Memo   This RFC is a discussion of the Pcmail workstation based distributed   mail system.  It is identical to the discussion inRFC-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   unlimited.Lambert                                                         [Page 1]

RFC 1056                         PCMAIL                        June 19882. 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   inappendix 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 mailLambert                                                         [Page 2]

RFC 1056                         PCMAIL                        June 1988   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   adequate mail service without hampering its performance on more   resource-rich workstations. Finally, all workstations have some   common characteristics that Pcmail should take advantage of.  For   instance, 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   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 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   locally.  When the client is next connected to the repository, the   changes are executed, 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 workstation as a client.  Mail messages are split into twoLambert                                                         [Page 3]

RFC 1056                         PCMAIL                        June 1988   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 anRFC-822 standard message header.  While   the client may not have enough storage to hold a complete set of   messages, it can usually hold a complete set of descriptors, thus   providing the user with at least a summary of his mail state.  For   clients with extremely limited resources, Pcmail allows the storage   of partial sets of descriptors.  Although this means the user does   not have a complete local mail state, he can at least look at   summaries of some messages.  In the cases where the client cannot   immediately store message bodies, it can always pull them over from   the repository as storage becomes available.   The remainder of this document is broken up into sections discussing   the following:      - The repository architecture      - DMSP, its operations, and motivation for its design      - The client architecture      - A typical DMSP session between the repository and a        client      - The current Pcmail implementation      - Appendices describing the DMSP protocol in detail3. Repository architecture   A typical machine running repository code has a relatively powerful   processor and a large amount of disk storage.  It must also be a   permanent network site, for two reasons.  First, clients communicate   with the repository over a network, and rely on the repository's   being available at any time.  Second, people sending mail to   repository users rely on the repository's being available to receive   mail at any time.   The repository must perform several tasks.  First, and most   importantly, the repository must efficiently manage a potentially   large number of users and their mail states.  Mail must be reliably   stored in a manner that makes it easy for multiple clients to access   the global mail state and synchronize their local mail states with   the global state.  Since a large category of electronic mail is   represented by bulletin boards (bboards), the repository should   efficiently manage bboard mail, using a minimum of storage to storeLambert                                                         [Page 4]

RFC 1056                         PCMAIL                        June 1988   bboard messages in a manner that still allows any user subscribing to   the bboard to read the mail.  Second, the repository must be able to   communicate efficiently with its clients.  The protocol used to   communicate between repository and client must be reliable and must   provide operations that (1) allow typical mail manipulation, and (2)   support Pcmail's distributed nature by allowing efficient   synchronization between local and global mail states.  Third, the   repository must be able to process mail from sources outside the   repository's own user community (a primary outside source is the   Internet).  Internet mail will arrive with a NICRFC-822 standard   message header; the recipient names in the message must be properly   translated from theRFC-822 namespace into the repository's   namespace.3.1. Management of user mail state   Pcmail divides the world into a community of users.  Each user is   associated with a user object.  A user object consists of a unique   name, a password (which the user's clients use to authenticate   themselves to the repository before manipulating a global mail   state), a list of "client objects" describing those clients belonging   to the user, a list of "subscription objects", and a list of "mailbox   objects".   A client object consists of a unique name and a status.  A user has   one client object for every client he owns; a client cannot   communicate with the repository unless it has a corresponding client   object in a user's client list.  Client objects therefore serve as a   means of identifying valid clients to the repository.  Client objects   also allow the repository to manage local and global mail state   synchronization; the repository associates with every client an   "update list" of message state changes which have occurred since the   client's last synchronization.   A client's status is either "active" or "inactive".  The repository   defines inactive clients as those clients which have not connected to   the repository within a set time period (one week in the current   repository implementation).  When a previously-inactive client does   connect to the repository, the repository notifies the client that it   has been inactive for some time and should "reset" itself.  Resetting   a client has the effect of placing every message in every mailbox   onto the client's update list.  This allows the client to get a fresh   global mail state from the repository when it next synchronizes (see   synchronization discussion following).  The reset is performed on the   assumption that enough global state changes occur in a week that the   client would spend too much time performing an ordinary local state-   global state synchronization.Lambert                                                         [Page 5]

RFC 1056                         PCMAIL                        June 1988   Messages are stored in mailboxes.  Users can have any number of   mailboxes, which serve both to store and to categorize messages.  A   mailbox object both names a mailbox and describes its contents.   Mailboxes are identified by a unique name; their contents are   described by three numeric values.  The first is the total number of   messages in the mailbox, the second is the total number of unseen   messages (messages that have never been seen by the user via any   client) in the mailbox, and the third is the mailbox's next available   message unique identifier (UID).  The above information is stored in   the mailbox object to allow clients to get a summary of a mailbox's   contents without having to read all the messages within the mailbox.   Some mailboxes are special, in that other users may read the messages   stored in them.  These mailboxes are called "bulletin board   mailboxes" or "bboard mailboxes".  The repository uses bboard   mailboxes to store bboard mail.  Bboard mailboxes differ from   ordinary mailboxes in the following ways:      - Their names are unique across the entire repository;        for instance, only one bboard mailbox named "sf-lovers"        may exist in the entire repository community.  This        does not preclude other users from having an ordinary        mailbox named "sf-lovers".      - Subscribers to the bboard are granted read-only access        to the messages in the bboard mailbox.  The bboard        mailbox's owner (typically the system manager) has        read/update/delete access to the mailbox.   A bboard subscriber keeps track of the messages he has looked at via   a subscription object.  The subscription object contains the name of   the bboard, its owner (the user who owns the bboard mailbox where all   the messages are stored), and the UID of the first message not yet   seen by the subscriber.   Users gain read-only access to a bboard by creating a subscription to   it; they lose that access when they delete that subscription.  A list   of all bboard mailboxes available for subscription can be transmitted   to the user on demand.   Associated with each mailbox are any number of message objects.  Each   message is broken into two parts--a "descriptor", which contains a   summary of useful information about the message, and a "body", which   is the message text itself, including its NICRFC-822 message header.   Each message is assigned a monotonically increasing UID based on the   owning mailbox's next available UID.  Each mailbox has its own set of   UIDs which, together with the mailbox name and user name, uniquely   identify the message within the repository.  A descriptor holds theLambert                                                         [Page 6]

RFC 1056                         PCMAIL                        June 1988   following information:  the message UID, the message size in bytes   and lines, four "useful" message header fields (the "date:", "to:",   "from:", and "subject:" fields), and sixteen flags.  These flags are   given identifying numbers 0 through 15.  Eight of these flags have   well-known definitions and are reserved for the repository's use.   The eight repository-defined flags mark:      - (#0) whether the message has been deleted      - (#1) whether it has been seen      - (#2) whether it has been forwarded to the user      - (#3) whether it has been forwarded by the user      - (#4) whether it has been filed (written to a text file        outside the repository)      - (#5) whether it has been printed (locally or remotely)      - (#6) whether it has been replied to      - (#7) whether it has been copied to another mailbox   The remaining eight flags are availble for user use.  Descriptors   serve as an efficient means for clients to get message information   without having to waste time retrieving the entire message from the   repository.3.2. Repository-to-RFC-822 name translation   "Address objects" provide the repository with a means for translating   theRFC-822-style mail addresses in Internet messages into repository   names.  The repository provides its own namespace for message   identification.  Any message is uniquely identified by the triple   (user-name, mailbox-name, message-UID).  Any mailbox is uniquely   identified by the pair (user-name, mailbox-name).  In order to   translate betweenRFC-822-style mail addresses and repository names,   the repository maintains a list of address objects.  Each address   object is an association between anRFC-822-style address and a   (user-name, mailbox-name) pair.  When mail arrives from the Internet,   the repository can use the address object list to translate the   recipients into (user-name, mailbox-name) pairs and route the message   correctly.Lambert                                                         [Page 7]

RFC 1056                         PCMAIL                        June 19884. Communication between repository and client: DMSP   The Distributed Mail System Protocol (DMSP) defines and manipulates   the objects mentioned in the previous section.  It has been designed   to work with Pcmail's singlerepository/multiple-client model of the   world.  In addition to providing typical mail manipulation functions,   DMSP provides functions that allow easy synchronization of global and   local mail states.   DMSP has been completely re-specified in this version of Pcmail.   Formerly, DMSP was implemented on top of the USP remote-procedure-   call protocol.  Since this protocol is not fully unofficially   specified (let alone officially specified) anywhere, implementation   of USP is difficult for sites wishing to implement Pcmail on   different systems.  We therefore have decided to completely redesign   DMSP.  It is now a very simple request/response protocol similar to   SMTP or NNTP, running directly on a reliable bidirectional byte-   stream such as TCP.  The TCP contact port for DMSP has been   designated 158.  Requests and responses consist of ASCII characters;   on octet-based transmission streams, each character is transmitted   rightjustified in an octet with the high-order bit cleared to zero.4.1. DMSP commands   DMSP operations consist of an operation name, followed by zero or   more tab or space characters, followed by zero or more arguments,   each of which is separated from the operation name and other   arguments by one or more space or tab characters.  All operation   requests, as well as all responses, must be terminated with a   carriage-return plus line-feed (CR-LF) pair.  All operation names and   arguments must be taken from the set of alphanumeric characters plus   the characters dash ("-"), underscore ("_"), and period (".").   DMSP operation names are case-insensitive; they may be transmitted in   any combination of upper and lower case.  DMSP arguments are case-   insensitive but case-preserving; in other words a mailbox named   "MarkL" may be referred to by an operation argument "markl", but will   always be stored, and transmitted in a repository response, as   "MarkL"; furthermore, any attempt to create a new mailbox "MaRkL"   will not be permitted.   Each operation argument may contain no more than 64 characters.  No   single request or response line may contain more than 512 characters,   including all white space and the terminating CR-LF.4.2. DMSP responses   A DMSP operation always results in a response, which may be followedLambert                                                         [Page 8]

RFC 1056                         PCMAIL                        June 1988   in turn by a list, consisting of zero or more lines of CR-LF-   terminated text terminated by a single period (".") plus a CR-LF.  A   response is always prefaced by a three-digit reply code; possible   text following the response code can be in any format.  The response   code is sufficient to determine whether the operation succeeded or   failed, or whether more text is forthcoming following the response   line.  Any text following the response code is for information only,   and need not follow any particular format.   The first digit indicates whether the operation succeeded or failed,   and if it succeeded whether or not more text should be presented to   the repository.  Definitions of the first digit are similar to those   of NNTP:   1XX             Informative message   2XX             Operation completed successfully   3XX             Operation completed successfully, present                   remainder of text and terminate with a single                   period plus CR-LF pair.   4XX             Operation was performed and failed for some                   reason.   5XX             Operation could not be performed because of a                   protocol syntax error of some sort.   The second digit indicates the type of object referred to by the   response.   X0X             Miscellaneous   X1X             User operation   X2X             Client operation   X3X             Mailbox operationLambert                                                         [Page 9]

RFC 1056                         PCMAIL                        June 1988   X4X             Subscription operation   X5X             Message operation   X6X             Address operation   In an error response, the final digit can describe the type of error   that occurred.  Otherwise, it simply gives a response a unique   number.  Numbers 0 through 3 are significant in 4XX-class (error)   responses only.  Numbers 0-9 in all other responses serve only to   differentiate responses dealing with the same type of object under   different circumstances.   4X0             Operation failed because object exists   4X1             Operation failed because object does not exist   4X2             Operation failed because of an internal error   4X3             Operation failed because of an argument syntax                   error   Each operation generates one of a set of responses, detailed in the   protocol specification appendix.   List termination is determined solely by a well-known character   sequence (CR-LF, period, CR-LF).  Since application data could well   accidentally contain this termination sequence, the transmitting   protocol module must modify application data so it contains no   termination sequences.  The receiving module must similarly undo the   modification before presenting the data to the application at the   receiving end.   The transmitting module modifies application data as follows:  If a   line of application data begins with a period, that period is   duplicated.  Since the termination sequence is a single period,   accidental termination has now been prevented.   The receiving protocol checks incoming all incoming data lines for a   leading period.  A single period is a list terminator; a period   followed by other text is removed before being presented to theLambert                                                        [Page 10]

RFC 1056                         PCMAIL                        June 1988   receiving application.4.3. DMSP sessions   A DMSP session proceeds as follows: a client begins the session with   the repository by opening a connection to the repository's machine.   The client then authenticates both itself and its user to the   repository with a "login" operation.  If the authentication is   successful, the user performs an arbitrary number of DMSP operations   before ending the session with a "logout" operation, at which time   the connection is closed by the repository.   Because DMSP can manipulate a pair of mail states (local and global)   at once, it is extremely important that all DMSP operations are   failure-atomic.  Failure of any DMSP operation must leave both states   in a consistent, known state.  For this reason, a DMSP operation is   defined to have failed unless an explicit acknowledgement is received   by the operation initiator.  This acknowledgement consists of a   response code possibly followed by information, as described above.   Following is a general discussion of all the DMSP operations.  The   operations are broken down by type: general operations, user   operations, client operations, mailbox operations, address   operations, subscription operations, and message operations.   Detailed operation specifications appear at the end of this document.4.4. General operations   The first group of DMSP operations perform general functions that   operate on no one particular class of object.  DMSP has three general   operations which provide the following services:   In order to prevent protocol version skew between clients and the   repository, DMSP provides a "send-version" operation.  The client   supplies its DMSP version number as an argument; the operation   succeeds if the supplied version number matches the repository's DMSP   version number.  It fails if the two version numbers do not match.   The version number is a natural number like "100", "101", "200".  The   "send-version" operation should be the first that a client sends to   the repository, since no other operation may work correctly if the   client and repository are using different versions of DMSP.   Users can send mail to other users via the "send-message" operation.   The message must have an Internet-style header as defined by NICRFC-822.  The repository takes the message and distributes it to the   mailboxes specified by the message header's destination fields.  If   one or more of the mailboxes exists outside the repository's user   community, the repository is responsible for handing the message to aLambert                                                        [Page 11]

RFC 1056                         PCMAIL                        June 1988   local SMTP server.  The message envelope is generated by the   repository from the message contents since it may be difficult for   some clients to perform envelope-generation functions such as address   verification and syntax checking.   A success acknowledgement is sent from the repository only if (1) the   entire message was successfully transmitted from client to   repository, and (2) the message header was properly formatted.  Once   the repository has successfully received the message from the client,   any subsequent errors in queueing or delivery must be noted via   return mail to the user.   The last general operation is the "help" operation.  The repository   responds to "help" by printing an acknowledgement followed by a list   of supported commands, terminated with a period plus CR-LF.  The   information is intended for display and can be in any format as long   as the individual lines of text returned by the repository are CR-   LF-terminated.4.5. User operations   The next series of DMSP operations manipulates user objects.  The   most common of these operations are "login" and "logout".  A client   must perform a login operation before being able to access a user's   mail state.  A DMSP login operation takes five arguments: (1) the   user's name, (2) the user's password, (3) the name of the client   performing the login, (4) a flag set to 1 if the repository should   create a client object for the client if one does not exist (0 else),   and (5) a flag set to 1 if the client wishes to operate in "batch   mode" and 0 if the client wishes to operate in "interactive" mode.   The last flag value allows the repository to tune internal parameters   for either mode of operation.   The repository can make one of three responses.  First, it can make a   success response, indicating successful authentication.  Second, it   can make one of several failure responses, indicating failed   authentication.  Finally, it can make a special response indicating   that authentication was successful, but that the client has not been   used in over a week.  This last response serves as a hint that the   client should consider erasing its local mail state and pulling over   a complete version of the repository's mail state.  This is done on   the assumption that so many mail state changes have been made in a   week that it would be inefficient to perform a normal   synchronization.   When a client has completed a session with the repository, it   performs a logout operation.  This allows the repository to perform   any necessary cleanup before closing the network connection.Lambert                                                        [Page 12]

RFC 1056                         PCMAIL                        June 1988   A user can change his password via the "set-password" operation.  The   operation works much the same as the UNIX change-password operation,   taking as arguments the user's current password and a desired new   password.  If the current password given matches the user's current   password, the user's current password is changed to the new password   given.  Because encryption can be difficult to perform on some   resource-poor clients, passwords are transmitted in clear text.   Clearly this is not an acceptable long-term solution, and   alternatives are welcomed.4.6. Client operations   DMSP provides four operations to manipulate client objects.  The   first, "list-clients", tells the repository to send the user's client   list to the requesting client.  The list is a series of lines, one   per client, containing the client's name, followed by whitespace,   followed by a status string.  The status is either "inactive" or   "active".  As with all text responses, the list is terminated with a   period plus CR-LF.   The "create-client" operation allows a user to add a client object to   his list of client objects.  Although the login operation duplicates   this functionality via the "create-this- client?" flag, the create-   client operation is a useful means of creating a number of new client   objects while logged into the repository via an existing client.  The   create-client operation requires as an argument the name of the   client to create.   The "delete-client" operation removes an existing client object from   a user's client list.  The client being removed cannot be in use by   anyone at the time.  Delete-client also requires as an argument the   name of the client to delete.   The last client operation, "reset-client", causes the repository to   place all of the messages in all mailboxes onto the named client's   update list.  When a client next synchronizes with the repository, it   will end up receiving a list of all descriptors when it requests a   list of changed message descriptors for a particular mailbox.  This   is useful for two reasons.  First, a client's local mail state could   easily become lost or damaged, especially if it is stored on a floppy   disk.  Second, if a client has been marked as inactive by the   repository, the reset-client operation provides a fast way of   resynchronizing with the repository, assuming that so many   differences exist between the local and global mail states that a   normal synchronization would take far too much time.Lambert                                                        [Page 13]

RFC 1056                         PCMAIL                        June 19884.7. Mailbox operations   DMSP supports seven operations that manipulate mailbox objects.   First, "list-mailboxes" has the repository send to the requesting   client information on each mailbox.  The repository transmits one   line of information per mailbox, terminating the list with a period   plus CR-LF.  Each line contains, in order and separated by   whitespace, the mailbox name, "next available UID", total message   count, and unseen message count.  This operation is useful in   synchronizing local and global mail states, since it allows a client   to compare the user's global mailbox list with a client's local   mailbox list.  The list of mailboxes also provides a quick summary of   each mailbox's contents without having the contents present.   The "create-mailbox" has the repository create a new mailbox and   attach it to the user's list of mailboxes.  It takes as an argument   the name of the mailbox to create.   "Delete-mailbox" removes a mailbox from the user's list of mailboxes.   All messages within the mailbox are also deleted and permanently   removed from the system.  Any address objects binding the mailbox   name toRFC-822-style mailbox addresses are also removed from the   system.  Delete-mailbox takes as an argument the name of the mailbox   to delete.   "Create-bboard-mailbox" allows a user to create a bboard mailbox.   The name given as an argument must be unique across the entire   repository user community.  Once the bboard mailbox has been created,   other users may subscribe to it, using subscription objects to keep   track of which messages they have read on which bboard mailboxes.   "Delete-bboard-mailbox" allows a bboard's owner to delete a bboard   mailbox.  Subscribers who attempt to read from a bboard mailbox after   it has been deleted are told that the bboard no longer exists.   Again, the operation's argument is the name of the bboard mailbox to   delete.   "Reset-mailbox" causes the repository to place all of the messages in   a named mailbox onto the current client's update list.  When the   client next requests a list of changed message descriptors for this   mailbox, it will receive a list of all message descriptors in the   mailbox.  This operation is merely a more specific version of the   reset-client operation (which allows the client to pull over a   complete copy of the user's global mail state).  Its primary use is   for mailboxes whose contents have accidentally been destroyed   locally.   Finally, DMSP has an "expunge-mailbox" operation.  Any message can beLambert                                                        [Page 14]

RFC 1056                         PCMAIL                        June 1988   deleted and "undeleted" at will, since this simply changes the value   of a flag attached to the message.  Deletions are made permanent by   performing an expunge-mailbox operation.  The expunge operation   causes the repository to look through a named mailbox, removing from   the system any messages marked "deleted".  Expunge-mailbox takes as   an argument the name of the mailbox to expunge.4.8. Address operations   DMSP provides three operations that allow users to manipulate address   objects.  First, the "list-address" operation returns a list of   address objects associated with a particular mailbox.  Each address   is transmitted on a separate line terminated by a CR-LF; the list is   terminated with a period plus CR-LF.   The "create-address" operation adds a new address object that   associates a (user-name, mailbox-name) pair with a givenRFC-822-   style mailbox address.  It takes as arguments the mailbox name and   the address name.   Finally, the "delete-address" operation destroys the address object   binding the givenRFC-822-style mail address and the given (user-   name, mailbox-name) pair.  Arguments are the address to delete and   the mailbox it belongs to.4.9. Subscription operations   DMSP provides five subscription operations.  The first, "list-   subscriptions", gives the user a list of the bboards he is currently   subscribing to.  The list consists of one line of information per   subscription.  Each entry contains the following information, in   order:      - The bulletin board's name      - The UID of the first message the subscriber has not yet        seen      - The number of messages the subscriber has not yet seen      - The highest message UID in the bulletin board   "List-available-subscriptions" gives the user a list of all bboards   he can subscribe to.  The list consists of bboard names, one per   line, terminated by a period plus CR-LF.  "Createsubscription" adds a   subscription to the user's list of subscriptions; it takes as an   argument the name of the bboard to subscribe to.  "Delete-   subscription" removes a subscription from the list, and takes as anLambert                                                        [Page 15]

RFC 1056                         PCMAIL                        June 1988   argument the name of the subscription to remove.  Note that this does   not delete the associated bboard mailbox (obviously only the bboard's   owner can do that).  It merely removes the user from the list of the   bboard's subscribers.  Finally DMSP allows the user to tell the   repository which messages in a bboard he has seen.  Every   subscription object contains the UID of the first message the user   has not yet seen; the "reset-subscription" operation updates that   number, insuring that the user sees a given bboard message only once.   Reset-subscription takes as arguments the name of the subscription   and the new UID value.4.10. Message operations   The most commonly-manipulated Pcmail objects are messages; DMSP   therefore provides special message operations to allow efficient   synchronization, as well as a set of operations to perform standard   message-manipulation functions.   A user may request a series of descriptors with the "fetch-   descriptors" operation.  The series is identified by a pair of   message UIDs, representing the lower and upper bounds of the list.   Since UIDs are defined to be monotonically increasing numbers, a pair   of UIDs is sufficient to completely identify the series of   descriptors.  If the lower bound UID does not exist, the repository   starts the series with the first message with UID greater than the   lower bound.  Similarly, if the upper bound does not exist, the   repository ends the series with the last message with UID less than   the upper bound.  If certain UIDs within the series no longer exist,   the repository obviously does not send them.  The repository returns   the descriptors in a list with the following format:   If a descriptor has been expunged, the repository transmits two   consecutive lines of information: the word "expunged" on one line,   followed by the message UID on the next line.  "Expunged"   notifications are only transmitted in response to a "fetch-changed-   descriptors" command; they are an indication to the client that   someone else has expunged the mailbox and that the client should   remove the local copy of the expunged message.   If a descriptor has not been expunged, it is presented as six   consecutive lines of information: the word "descriptor" on the first   line, followed by a second line containing the message UID, flag   states (see examples following), message length in bytes, and message   length in lines, followed by four lines containing in order the   message "from:" field, "to:" field, "date:" field, and "subject:"   field.  The entire list of descriptors is terminated by a period plus   CR-LF; individual descriptors are not specially terminated since the   first line ("expunged" or "descriptor") of a list entry determinesLambert                                                        [Page 16]

RFC 1056                         PCMAIL                        June 1988   the exact length of the entry (two lines or six lines).   The "fetch-changed-descriptors" operation is intended for use during   state synchronization.  Whenever a descriptor changes state (one of   its flags is cleared, for example), the repository notes those   clients which have not yet recorded the change locally.  Fetch-   changed-descriptors has the repository send to the client a maximum   of the first N descriptors which have changed since the client's last   synchronization, where N is a number sent by the client.  The list   sent begins with the descriptor with lowest UID.  Note that the list   of descriptors is only guaranteed to be monotonically increasing for   a given call to "fetch-changed-descriptors"; messages with lower UIDs   may be changed by other clients in between calls to "fetch-   changeddescriptors".  "Fetch-changed-descriptors" takes two   arguments:  the name of the mailbox to search, and the maximum number   of descriptors for the repository to return.   Once the changed descriptors have been looked at, a user will want to   inform the repository that the current client has recorded the change   locally.  The "reset-descriptors" command causes the repository to   mark as "recorded by current client" a given series of descriptors.   The series is identified by a low UID and a high UID.  UIDs within   the series that no longer exist are ignored.  Arguments are: mailbox   name, low UID in range, and high UID in range.   Whole messages are transmitted from repository to user with the   "fetch-message" operation.  The separation of "fetchdescriptors" and   "fetch-message" operations allows clients with small amounts of disk   storage to obtain a small message summary (via "fetch-descriptors" or   "fetch-changed-descriptors") without having to pull over the entire   message.  Arguments are mailbox name, followed by message UID.   Frequently, a message may be too large for some clients to store   locally.  Users can still look at the message contents via the   "print-message" operation.  This operation has the repository send a   copy of the message to a named printer.  The printer name need only   have meaning to the particular repository implementation; DMSP   transmits the name only as a means of identification.  Arguments are:   mailbox name, followed by message UID, followed by printer   identification.   Copying of one message into another mailbox is accomplished via the   "copy-message" operation.  A descriptor list of length one,   containing a descriptor for the copied message, is returned if the   copy operation is successful.  This descriptor is required because   the copied message acquires a UID different from the original   message.  The client cannot be expected to know which UID has been   assigned the copy, hence the repository's sending a descriptorLambert                                                        [Page 17]

RFC 1056                         PCMAIL                        June 1988   containing the UID.  Arguments to copy-message are:  source mailbox   name, target mailbox name, and source message UID.   Each message has associated with it sixteen flags, as described   earlier.  These flags can be set and cleared using the "set-message-   flag" operation.  The first eight flags have special meaning to the   repository as described above; the remaining eight are for user use.   Set-message-flag takes four arguments: mailbox name, message UID,   flag number (0 through 15), and desired flag state (0 or 1).5. Client Architecture   Clients can be any of a number of different workstations; Pcmail's   architecture must therefore take into account the range of   characteristics of these workstations.  First, most workstations are   much more affordable than the large computers currently used for mail   service.  It is therefore possible that a user may well have more   than one.  Second, some workstations are portable and they are not   expected to be constantly tied into a network.  Finally, many of the   smaller workstations resource-poor, so they are not expected to be   able to store a significant amount of state information locally.  The   following subsections describe the particular parts of Pcmail's   client architecture that address these different characteristics.5.1. Multiple clients   The fact that Pcmail users may own more than one workstation forms   the rationale for the multiple client model that Pcmail uses.  A   Pcmail user may have one client at home, another at an office, and   maybe even a third portable client.  Each client maintains a separate   copy of the user's mail state, hence Pcmail's distributed nature.   The notion of separate clients allows Pcmail users to access mail   state from several different locations.  Pcmail places no   restrictions on a user's ability to communicate with the repository   from several clients at the same time.  Instead, the decision to   allow several clients concurrent access to a user's mail state is   made by the repository implementation.5.2. Synchronization   Some workstations tend to be small and fairly portable; the   likelihood of their always being connected to a network is relatively   small.  This is another reason for each client's maintaining a local   copy of a user's mail state.  The user can then manipulate the local   mail state while not connected to the network (and the repository).   This immediately brings up the problem of synchronization between   local and global mail states.  The repository is continually in a   position to receive global mail state updates, either in the form ofLambert                                                        [Page 18]

RFC 1056                         PCMAIL                        June 1988   incoming mail, or in the form of changes from other clients.  A   client that is not always connected to the net cannot immediately   receive the global changes.  In addition, the client's user can make   his own changes on the local mail state.   Pcmail's architecture allows fast synchronization between client   local mail states and the repository's global mail state.  Each   client is identified in the repository by a client object attached to   the user.  This object forms the basis for synchronization between   local and global mail states.  Some of the less common state changes   include the adding and deleting of user mailboxes and the adding and   deleting of address objects.  Synchronization of these changes is   performed via DMSP list operations, which allow clients to compare   their local versions of mailbox and address object lists with the   repository's global version and make any appropriate changes.  The   majority of possible changes to a user's mail state are in the form   of changed descriptors.  Since most users will have a large number of   messages, and message states will change relatively often, special   attention needs to be paid to message synchronization.   An existing descriptor can be changed in one of three ways:  first,   one of its sixteen flag values can be changed (this encompasses the   user's reading an unseen message, deleting a message, printing a   message, etc).  Second, a descriptor can be created, either by the   delivery of a new message or by the copying of a message from one   mailbox to another.  Finally, a descriptor can be destroyed, via an   "expunge-mailbox" operation.   In the above cases, synchronization is required between the   repository and every client that has not previously noted the change.   To keep track of which clients have noticed a global mail state   change and changed their local states accordingly, each mailbox has   associated with it a list of active clients.  Each client has a   (potentially empty) "update list" of messages which have changed   since that client last synchronized.   When a client connects to the repository, it executes a DMSP "fetch-   changed-descriptors" operation.  This causes the repository to return   a list of all descriptors on that client's update list.  When the   client receives the changed descriptors, it may do one of two things:   if the descriptor is marked "expunged", it can remove the   corresponding message from the local mailbox.  If the descriptor is   not expunged, the client can store the descriptor, thus updating the   local mail state.  After a changed descriptor has been recorded, the   client uses the DMSP "reset-descriptors" operation to remove   descriptors from its update list.  Those descriptors will now not be   sent to the client unless (1) it is explicitly requested via a   "fetch-descriptors" operation, or (2) it changes again.Lambert                                                        [Page 19]

RFC 1056                         PCMAIL                        June 1988   In this manner, a client can run through its user's mailboxes,   getting all changes, incorporating them into the local mail state,   and marking the changes as recorded.5.3. Batch operation versus interactive operation   Because of the portable nature of some workstations, they may not   always be connected to a network (and able to communicate with the   repository).  Since each client maintains a local mail state, Pcmail   users can manipulate the local state while not connected to the   repository.  This is known as "batch" operation, since all changes   are recorded by the client and made to the repository's global state   in a batch, when the client next connects to the repository.   Interactive operation occurs when a client is always connected to the   repository.  In interactive mode, changes made to the local mail   state are also immediately made to the global state via DMSP   operations.   In batch mode, interaction between client and repository takes the   following form: the client connects to the repository and sends over   all the changes made by the user to the local mail state.  The   repository changes its global mail state accordingly.  When all   changes have been processed, the client begins synchronization; this   incorporates newly-arrived mail, as well as mail state changes by   other clients, into the local state.   In interactive mode, since local changes are immediately propagated   to the repository, the first part of batch-type operation is   eliminated.  The synchronization process also changes; although one   synchronization is required when the client first opens a connection   to the repository, subsequent synchronizations can be performed   either at the user's request or automatically every so often by the   client.5.4. Message summaries   Smaller workstations may have little in the way of disk storage.   Clients running on these workstations may never have enough room for   a complete local copy of a user's global mail state.  This means that   Pcmail's client architecture must allow user's to obtain a clear   picture of their mail state without having all their messages   present.   Descriptors provide message information without taking up large   amounts of storage.  Each descriptor contains a summary of   information on a message.  This information includes the message UID,   its length in bytes and lines, its status (contained in the eight   system-defined and eight user-defined flags), and portions of itsLambert                                                        [Page 20]

RFC 1056                         PCMAIL                        June 1988RFC-822 header (the "from:", "to:", "date:" and "subject:"  fields).   All of this information can be encoded in a small (around 100 bytes)   data structure whose length is independent of the size of the message   it describes.   Most clients should be able to store a complete list of message   descriptors with little problem.  This allows a user to get a   complete picture of his mail state without having all his messages   present locally.  If a client has extremely limited amounts of disk   storage, it is also possible to get a subset of the descriptors from   the repository.  Short messages can reside on the client, along with   the descriptors, and long messages can either be printed via the DMSP   print-message operation, or specially pulled over via the fetch-   message operation.6. Typical interactive-style client-repository interaction   The following example describes a typical communication session   between the repository and a client mail reader.  The client is one   of three belonging to user "Fred".  Its name is "office-client", and   since Fred has used the client within the last week, it is marked as   "active".  Fred has two mailboxes:  "fred" is where all of his   current mail is stored; "archive" is where messages of lasting   importance are kept.  The example will run through a simple   synchronization operation.  Typically, the synchronization will be   performed by a mail reader as part of a "get new mail" operation.   First Fred's mail reader connects to the repository and receives the   following banner:       200 Pcmail repository version 3.0.0 ready   In order to access his global mail state, the mail reader must   authenticate Fred to the repository; this is done via the DMSP login   operation:       login fred fred-password office-client 0 0   This tells the repository that Fred is logging in via "office-   client", and that "office-client" is identified by an existing client   object in Fred's mail state.  The first argument to the login   operation is Fred's repository user name.  The second argument is   Fred's password.  The third argument is the name of the client   communicating with the repository.  The fourth argument tells the   repository not to create "office-client" even if it cannot find its   client object.  The final argument tells the repository that Fred's   client is not operating in batch mode but rather in interactive mode.Lambert                                                        [Page 21]

RFC 1056                         PCMAIL                        June 1988   Fred's authentication checks out, so the repository logs him in.       200 command OK   Now that Fred is logged in, the mail reader performs an initial   synchronization.  This process starts with the mail reader's asking   for an up-to-date list of mailboxes:       list-mailboxes   The repository replies with:       230 mailbox list follows:       fred 2313 10 1       archive 101 100 0       .   This tells the mail reader that there are two mailboxes, "fred" and   "archive".  "Fred" has 10 messages, one of which is unseen.  The next   incoming message will be assigned a UID of 2313.  "Archive", on the   other hand, has 100 messages, none of which are unseen.  The next   message sent to "archive" will be assigned the UID 101.  There are no   new mailboxes in the list (if there were, the mail reader would   create them.  On the other hand, if some mailboxes in the mail   reader's local list were not in the repository's list, the program   would assume them deleted by another client and delete them locally   as well).   To synchronize, the mail reader need only look at each mailbox's   contents to see if (1) any new mail has arrived, or (2) if Fred   changed any messages on one of his other two clients subsequent to   "office-client"'s last connection to the repository.   The mail reader asks for any changed descriptors via the "fetch-   changed-descriptors" operation.  It requests at most ten changed   descriptors since storage is very limited on Fred's workstation.       fetch-changed-descriptors fred 10   The repository responds with:       250 descriptor list follows:       expungedLambert                                                        [Page 22]

RFC 1056                         PCMAIL                        June 1988       2101       expunged       2104       descriptor       2107 1100011100000010 1400 30       foo@bar.edu (Foo Jones)       fred@PTT.LCS.MIT.EDU       Wed, 9 Dec 87 10:43:52 EST       A typical subject line       descriptor       2312 0000000000000000 12232 320       joe@athena.mit.edu       fred@PTT.LCS.MIT.EDU       Thu, 17 Dec 87 18:24:09 PST       Another typical subject line       .   If a descriptor changed because it was expunged, it is transmitted as   two lines: the word "expunged" on one line, followed by the message   UID on the next line.  If one of its flags changed state, or it is a   new message, it is transmitted as six lines: the word "descriptor" on   one line, followed by a line containing the message UID, flags, and   length in bytes and lines, followed by the to, from, date, and   subject fields, each on one line.  The flags are transmitted as a   single string of ones and zeroes, a one if the flag is on and a zero   if the flag is off.  All 16 flags are always transmitted.  Flag   zero's state is the first character in the flag string; flag   fifteen's is the last character in the flag string.   The first two descriptors in the list have been expunged, presumably   by Fred's expunging his mailbox on another client.  The mail reader   removes messages 2101 and 2104 from its local copy of mailbox "fred".   The next descriptor in the list is one which Fred marked for deletion   on another client yesterday.  The mail reader marks the local version   of the message as deleted.  The last descriptor in the list is a new   one.  The mail reader adds the descriptor to its local list.  Since   all changes to mailbox "fred" have now been recorded locally, the   update list can be reset:       reset-descriptors fred 1 2312   The repository responds with:       200 command OK   indicating that it has removed from "office-client"'s update list allLambert                                                        [Page 23]

RFC 1056                         PCMAIL                        June 1988   messages in mailbox "fred" with UIDs between 1 and 2312 inclusive (in   this case just two messages).  "Fred" has now been synchronized.  The   mail reader now turns to Fred's "archive" mailbox and asks for the   first ten changed descriptors.       fetch-changed-descriptors archive 10   The repository responds with:       250 descriptor list follows:       .   The zero-length list tells the mail reader that no descriptors have   been changed in "archive" since its last synchronization.  No new   synchronization needs to be performed.   Fred's mail reader is now ready to pull over the new message.  The   message is 320 lines long; there might not be sufficient storage on   "office-client" to hold the new message.  The mail reader tries   anyway:       fetch-message fred 2312   The repository begins transmitting the message:       251 message follows:       UID: 2312       From: joe@bar.mit.edu       To: fred@PTT.LCS.MIT.EDU       Date: Thu, 17 Dec 87 18:24:09 PST       Subject: Another typical subject line       Fred,       ...   Halfway through the message transmission, Fred's workstation runs out   of disk space.  Because all DMSP operations are defined to be   failure-atomic, the portion of the message already transmitted is   destroyed locally and the operation fails.  The mail reader informs   Fred that the message cannot be pulled over because of a lack of disk   space.  The synchronization process is now finished and Fred can   start reading his mail.  The new message that was too big to fit on   "office-client" will be marked "off line"; Fred can use the mailLambert                                                        [Page 24]

RFC 1056                         PCMAIL                        June 1988   reader to either remote-print it or delete and expunge other messages   until he has enough space to store the new message.   Since Fred is running in interactive mode, changes he makes to any   messages will immediately be transmitted into DMSP operations and   sent to the repository.  Depending on the mail reader implementation,   Fred will either have to execute a "synchronize" command periodically   or the client will synchronize for him automatically every so often.7. A current Pcmail implementation   The following section briefly describes a current Pcmail system that   services a small community of users.  The Pcmail repository runs   under UNIX on a DEC Microvax-II connected to the Internet.  The   clients run on IBM PCs, XTs, and ATs, as well as Sun workstations,   Microvaxes, and VAX-750s.7.1. IBM PC client code   Client code for the IBM machines operates only in batch mode.  Users   make local state changes in a mail reader; the changes are queued   until the user runs a network client program.  The program connects   to the repository, performs the queued changes, and synchronizes   local and global mail states.  The network client program then   disconnects from the repository.   The IBM PC client code has gone through several revisions since the   first Pcmail RFC was published.  What was once a fairly primitive and   cumbersome system has evolved into a system that makes excellent use   of the PC's limited resources and provides a fairly powerful, easy-   to-use mail reader.   Users access and modify their local mail state via a mail reader   written in the Epsilon text editor's EEL extension language.  Users   are given a variety of commands to operate on individual messages and   mailboxes, as well as to compose outgoing mail.   Synchronization and the processing of queued changes is performed by   a separate program, which the user runs as desired.  The program   takes any actions queued while operating the mail reader, and   converts them into DMSP operations.  All queued changes are made   before any synchronization is performed.  The program can be invoked   directly from the mail reader, without having to exit and restart.   The limitation of IBM PC client operation to batch mode was made   because of development environment limitations.  The mail reader   cannot work with the network code inside it because of the network   program architecture.  The only solution was to provide a two-partLambert                                                        [Page 25]

RFC 1056                         PCMAIL                        June 1988   client, one part of which read the mail and one part of which   interacted with the repository.  Although slightly cumbersome, the   two-program setup works quite well.7.2. UNIX client code   Client code for the Suns, Microvaxes, and VAX-750s runs on 4.2/4.3BSD   UNIX.  It is fully interactive, with a powerful mail reader inside   Richard Stallman's GNU-EMACS editor.  Since UNIX-based workstations   have a good deal of main memory and disk storage, no effort was made   to lower local mail state size by keeping message descriptors rather   than message text.   The local mail state consists of a number of BABYL-format mailboxes.   The interface is very similar to the RMAIL mail reader already   present in GNU-EMACS.   The mail reader communicates with the repository through network code   implemented in EMACS-LISP.  Changes to the local mail state are   immediately made on the repository; although the repository is fast,   there is a small noticeable delay in performing operations over the   network.   There is no provision for automatic synchronization whenever new mail   arrives or old mail is changed by another client.  Instead, users   must get any new mail explicitly.  A simple "notification" program   runs in the background and wakes up every minute to check for new   mail; when mail arrives, the user executes a command to get the new   mail, synchronizing the mailbox at the same time.7.3. Repository code   The repository is implemented in C on 4.2/4.3BSD UNIX.  Currently it   runs on DEC VAX-750s and Microvaxes, although other repositories will   soon be running on IBM RT machines and Sun workstations.  The   repository code is designed to allow several clients belonging to a   particular user to "concurrently" modify the user's state.  A locking   scheme prevents one client from modifying mail state while another   client is modifying the same state.8. Conclusions   Pcmail is now used by a small community of people at the MIT   Laboratory for Computer Science.  The repository design works well,   providing an efficient means of storing and maintaining mail state   for several users.  Its performance is quite good when up to ten   users are connected; it remains to be seen whether or not the   repository will be efficient at managing the state of ten or aLambert                                                        [Page 26]

RFC 1056                         PCMAIL                        June 1988   hundred times that many users.  Given sufficient disk storage, it   should be able to, since communication between different users'   clients and the repository is likely to be very asynchronous and   likely to occur in short bursts with long "quiet intervals" in   between as users are busy doing other things.   Members of another research group at LCS are currently working on a   replicated, scalable version of the repository designed to support a   very large community of users with high availability.  This   repository also uses DMSP and has successfully communicated with   clients that use the current repository implementation.  DMSP   therefore seems to be usable over several flavors of repository   design.   The IBM PC clients are very limited in the way of resources.  The   mail reader/editor combination is quite powerful, making local mail   state manipulation fairly easy.  Obviously a big performance   enhancement would be to provide a fully interactive client.  As it   is, batch-style synchronization is relatively time consuming due to   the low performance of the PCs.  The "batch-mode" that the PCs use   tends to be good for those PCs that spend a large percentage of their   time unplugged and away from a network.  It is somewhat inconvenient   for those PCs that are always connected to a network and could make   good use of an "interactive-mode" state manipulation.   The UNIX-based clients are more powerful and easier to use than their   PC counterparts.  Synchronization is much faster, and there is far   more functionality in the mail reader (having an interface that runs   within GNU-EMACS helps a lot in this respect).  Most of those people   using the Pcmail system use the UNIX-based client code.Lambert                                                        [Page 27]

RFC 1056                         PCMAIL                        June 1988I. DMSP Protocol Specification   Following are a list of DMSP operations by object type, together with   syntax, and possible responses.  Some responses may be followed by   zero or more lines of text, terminated by a single period plus CR-LF   pair.  Only success responses and common error responses are listed;   a complete list of possible responses follows this appendix.   Expressions in angle brackets (i.e.  <mailbox-name>) are   metalinguistic variables indicating a general request or response   form.  Operations with arguments have a sample invocation following   the operation syntax and response.   General operations:       HELP       100 Repository version xxx.  Following are supported:       HELP       SEND-VERSION       SEND-MESSAGE       LOGIN       LOGOUT       ...       FETCH-MESSAGE       COPY-MESSAGE       .       SEND-VERSION <version-number>       200 Command OK       500 version skew!       i.e. SEND-VERSION 230       SEND-MESSAGE       350 enter message; end with "."       To: markl       From: markl       Subject: a test message       this is a test message       .Lambert                                                        [Page 28]

RFC 1056                         PCMAIL                        June 1988   Repository responds:       200 Command OK       403 message syntax error   User operations:       LOGIN <user> <password> <client> <create-p> <batch-p>       200 Command OK       221 Client out of date by > 1 week       404 Bad password       405 Client <client-name> is locked       411 No user named <user-name>       421 Client <client-name> not found       i.e. LOGIN markl foo random-client-name 1 0       LOGOUT       200 Command OK       SET-PASSWORD <old-password> <new-password>       200 Command OK       404 Incorrect old password       i.e. SET-PASSWORD foo bar   Client operations:       LIST-CLIENTS       220 Client list <name> <status> follows:       client-1 active       client-2 inactive       client-3 active       ...       client-foobar active       .    Each line of the list contains a client name, followed by   whitespace, followed by the word "active" or the word "inactive",   indicating whether or not the client has connected to the repository   within the last week.Lambert                                                        [Page 29]

RFC 1056                         PCMAIL                        June 1988       CREATE-CLIENT <client-name>       200 Command OK       403 <client-name> is an illegal name       420 Client <client-name> exists       i.e. CREATE-CLIENT new-client       DELETE-CLIENT <client-name>       200 Command OK       421 Client <client-name> not found       405 Client <client-name> is locked       i.e. DELETE-CLIENT old-client       RESET-CLIENT <client-name>       200 Command OK       421 Client <client-name> not found       405 Client <client-name> is locked       i.e. RESET-CLIENT any-old-client   Mailbox operations:       LIST-MAILBOXES       230 Mbox list <name> <high-UID> <#msgs> <#new> follows:       mailbox-1 2338 8 1       mailbox-2 59 44 0       ...       mailbox-foobar 19 9 0       .   Each line of the list contains a mailbox name, followed by the   mailbox's next available unique identifier, followed by the number of   messages in the mailbox, followed finally by the number of unseen   messages in the mailbox.  Unseen messages are those whose descriptors   have flag #1 ("message has been seen") set to zero.       CREATE-MAILBOX <mailbox-name>       200 Command OK       403 <mailbox-name> is an illegal name       430 <mailbox-name> already exists       440 <mailbox-name> exists as a bboard subscriptionLambert                                                        [Page 30]

RFC 1056                         PCMAIL                        June 1988       i.e. CREATE-MAILBOX current-events       DELETE-MAILBOX <mailbox-name>       200 Command OK       431 mailbox <mailbox-name> not found       440 <mailbox-name> is a bboard; use delete-bboard-mailbox       i.e. DELETE-MAILBOX income-tax-information       CREATE-BBOARD-MAILBOX <mailbox-name>       200 Command OK       430 a mailbox named <mailbox-name> already exists.       430 a bboard mailbox named <mailbox-name> already exists.       403 <mailbox-name> is an illegal name       i.e. CREATE-BBOARD-MAILBOX sf-lovers       DELETE-BBOARD-MAILBOX <mailbox-name>       200 Command OK       404 not owner of <mailbox-name>       431 no bboard mailbox named <mailbox-name>       i.e. DELETE-BBOARD-MAILBOX rec.autos       RESET-MAILBOX <mailbox-name>       200 Command OK       431 mailbox <mailbox-name> not found       i.e. RESET-MAILBOX british-cars       EXPUNGE-MAILBOX <mailbox-name>       200 Command OK       431 mailbox <mailbox-name> not found       EXPUNGE-MAILBOX british-cars   Address operations:       LIST-ADDRESSES <mailbox-name>       260 Address list for <mailbox-name> follows:       address-1Lambert                                                        [Page 31]

RFC 1056                         PCMAIL                        June 1988       address-2       ...       address-6       .       or       431 mailbox <mailbox-name> not found       i.e. LIST-ADDRESSES archive       Each line of the list consists solely of one address.       CREATE-ADDRESS <mailbox-name> <address-name>       200 Command OK       403 <mailbox-name> is an illegal name       431 mailbox <mailbox-name> not found       460 <address-name> already exists       i.e. CREATE-ADDRESS markl markl-bug-pcmail       DELETE-ADDRESS <mailbox-name> <address-name>       200 Command OK       431 mailbox <mailbox-name> not found       461 address <address-name> not found       i.e. DELETE-ADDRESS markl markl-info-cobol   Subscription operations:       LIST-SUBSCRIPTIONS       240 subscription list follows:       bboard-1 2573 33 2606       bboard-2 541 4 545       ...       bboard-6 1530 43 1573       .   Each line of the list consists of a bulletin-board name, followed by   the UID of the first message which the user has not yet looked at,   followed by the number of messages in the bulletin-board that the   user has not yet looked at, followed by the bulletin-board's next   available unique message identifier.Lambert                                                        [Page 32]

RFC 1056                         PCMAIL                        June 1988       CREATE-SUBSCRIPTION <bboard-name>       200 Command OK       403 <bboard-name> is an illegal name       430 A mailbox named <bboard-name> already exists       431 Bboard mailbox <bboard-name> not found       440 Already subscribing to <bboard-name>       i.e. CREATE-SUBSCRIPTION sf-lovers       DELETE-SUBSCRIPTION <bboard-name>       200 Command OK       441 Subscription <bboard-name> not found       i.e. DELETE-SUBSCRIPTION rec.music       RESET-SUBSCRIPTION <bboard-name> <new-UID>       200 Command OK       441 Subscription <bboard-name> not found       i.e. RESET-SUBSCRIPTION rec.music.gdead 1210       LIST-AVAILABLE-SUBSCRIPTIONS       241 All available bboards follow:       mod.politics       sfl       tcp-ip       forum       ...       comp.emacs       .       Each line of the list consists solely of one bulletin-board       name.   Message operations:       FETCH-CHANGED-DESCRIPTORS <mailbox-name> <max-to-send>       250 Descriptor list follows:       expunged       2333       expunged       2334Lambert                                                        [Page 33]

RFC 1056                         PCMAIL                        June 1988       descriptor       2337 0001000001110000 481 14       croaker@ptt.lcs.mit.edu       fred@anymachine.mit.edu       Tue, 19 Jan 88 11:10:03 EST       a typical subject line       descriptor       2339 0000000000000000 1457 40       bob@lcs.mit.edu       csr-people@ptt.lcs.mit.edu       Mon, 18 Jan 88 13:08:17 +0000       another typical subject line       expunged       2340       .       or       431 mailbox <mailbox-name> not found       i.e. FETCH-CHANGED-DESCRIPTORS markl 100   Each element of the descriptor list is either two or six lines long.   Descriptors which have been expunged are transmitted as two lines:   the word "expunged" on one line, followed by the message unique   identifier on the next line.  Descriptors which still exist are   transmitted as six lines: the word "descriptor" on one line, followed   by a line containing the message unique identifier, flag states   (sixteen characters either one or zero depending on the associated   flag value), followed by the message length in characters, followed   by the message length in lines.  The next four lines contain the   message's "from:", "to:", "date:", and "subject:" fields,   respectively.  Flag zero's state is the first character in the flag   string; flag fifteen's is the last character in the flag string.       FETCH-DESCRIPTORS <mailbox-name> <low-uid> <high-uid>       250 Descriptor list follows:       descriptor       2337 0001000001110000 481 14       croaker@ptt.lcs.mit.edu       fred@anymachine.mit.edu       Tue, 19 Jan 88 11:10:03 EST       a typical subject line       descriptor       2339 0000000000000000 1457 40       bob@lcs.mit.edu       csr-people@ptt.lcs.mit.eduLambert                                                        [Page 34]

RFC 1056                         PCMAIL                        June 1988       Mon, 18 Jan 88 13:08:17 +0000       another typical subject line       .       or       431 mailbox <mailbox-name> not found       i.e. FETCH-DESCRIPTORS british-cars 12 31       COPY-MESSAGE <src-mailbox> <target-mailbox> <source-UID>       250 Descriptor list follows:       descriptor       2339 0000000000000000 1457 40       bob@lcs.mit.edu       csr-people@ptt.lcs.mit.edu       Mon, 18 Jan 88 13:08:17 +0000       another typical subject line       .       or       400 cannot copy message onto itself       431 target mailbox <target-mailbox> not found       431 source mailbox <source-mailbox> not found       451 message <source-UID> not found       i.e. COPY-MESSAGE markl british-cars 2338       RESET-DESCRIPTORS <mailbox-name> <low-UID> <high-UID>       200 Command OK       431 mailbox <mailbox-name> not found       i.e. RESET-DESCRIPTORS markl 1 10000       PRINT-MESSAGE <mailbox-name> <UID> <printer-ID>       200 Command OK       401 printer <printer-name> not found       431 mailbox <mailbox-name> not found       451 message <UID> not found       i.e. PRINT-MESSAGE markl 2433 pravdaLambert                                                        [Page 35]

RFC 1056                         PCMAIL                        June 1988       SET-MESSAGE-FLAG <mailbox-name> <UID> <flagnum> <state>       200 Command OK       431 mailbox <mailbox-name> not found       451 message <UID> not found       500 flag number <flag-number> out of range       i.e. SET-MESSAGE-FLAG british-cars 23 0 1       FETCH-MESSAGE <mailbox-name> <UID>       251 message follows:       From: markl@ptt.lcs.mit.edu       To: markl@ptt.lcs.mit.edu       Date: Sun, 17 Jan 88 11:11:11 EST       Subject: anything       this is a sample of some       message text       .       or       431 Mailbox <mailbox-name> not found       451 message <UID> not found       i.e. FETCH-MESSAGE current-events 495Lambert                                                        [Page 36]

RFC 1056                         PCMAIL                        June 1988II. Operations by name   copy-message   create-address   create-bboard-mailbox   create-client   create-mailbox   create-subscription   delete-address   delete-bboard-mailbox   delete-client   delete-mailbox   delete-subscription   expunge-mailbox   fetch-changed-descriptors   fetch-descriptors   fetch-message   help   list-addresses   list-available-subscriptions   list-clients   list-mailboxes   list-subscriptions   login   logout   print-message   reset-client   reset-descriptors   reset-mailbox   reset-subscription   send-message   send-version   set-message-flag   set-passwordLambert                                                        [Page 37]

RFC 1056                         PCMAIL                        June 1988III. Responses by number   100 Pcmail repository version XXX; following are supported   200 Command OK   220 Client list <name> <status> follows:   221 Client out of date by > 1 week   230 Mailbox list <name> <high UID> <#msgs> <#new> follows:   240 Subscription list follows:   250 Descriptor list follows:   251 Message follows:   260 Address list follows:   350 enter message; end with "."   400 cannot copy message onto itself   410 already logged in   420 client <name> already exists   430 mailbox <name> already exists   430 bboard mailbox <name> already exists   440 subscription <name> already exists   460 address <name> already exists   411 no user named <name>   421 client <name> not found   431 mailbox <name> not found   441 subscription <name> not found   451 message <UID> not found   461 address <name> not found   402 internal error message   403 syntax error in outbound message   404 bad password or permission denied   405 mail state is temporarily in use by another client   406 please log in   500 operation syntax error or illegal argumentLambert                                                        [Page 38]