RFC524

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Network Working Group J. White Request for Comments: 524 SRI-ARC NIC: 17140 13 June 1973


                     A Proposed Mail Protocol

AUTHOR'S INTENT

This is the document I offered in (15146,) to write. It's a proposed specification for handling mail in the Network -- a Mail Protocol.

Main handling is currently implemented as two FTP commands, MAIL and MLFL, which permit an FTP user process to deliver a file or string of text to an FTP server process, designating it as mail to be made available to a user, identified by a local name, in its host. The protocol proposed here is much richer than that, both in terms of the functions it supports, and in terms of the flexibility it provides.

Although one can (I think) and might, implement software on the basis of this document, this REALLY IS a Request for Comments. Comments, questions, position papers are solicited. There are, I'm sure, bugs in the protocol specified here, and I hope that readers will point them out via RFC as they discover them.

Various members of the Network community have, during the last few months, pointed out to me specific inadequacies in the existing mail commands and asked me to be conscious of them in designing a new protocol. I've tried to do that. If anyone feels that his concern wasn't properly dealt with here, or that it slipped through the cracks entirely (for which I apologize in advance), I would appreciate it if he would prod me once more.

INTRODUCTION

THE MAIL PROTOCOL ENVIRONMENT

  The Mail Protocol (MP) is implemented by Mail user and server
  processes, in keeping with the model for previous high-level
  protocols.  The Mail user and server processes are further
  specified to be also FTP user and server processes, respectively.
  That is, MP is implemented as a set of commands accessible from
  within the FTP command space.
  The MP command set is defined to lie conceptually within a
  subsystem, invoked from the FTP command space with the command
  MAIL <CFLF>.




     NOTE:  Since a command called 'MAIL' already exists within the
     FTP command space, the command name 'XMAIL' might substitute
     for 'MAIL' while the current mail commands are being phased
     out.
  The MP command set may or may not (according to the implementation
  of a particular server) be implemented by a process distinct from
  that which implements FTP proper.
  The following are implications of the 'subsystem' concept, of
  which the reader (and implementer) must be aware:
     (1) Names of MP commands are known only within the MP
     subsystem.  MP commands must (and should naturally) be rejected
     by the server if the user process presents them outside of the
     subsystem.
     (2) Exit from the Mail subsystem (to the FTP command space) is
     effected with and only with the command EXIT <CRLF>.  FTP
     commands must be rejected by the server if the user presents
     them while inside the subsystem (i.e., before EXIT is issued).
     (3) The same command name may be assigned without ambiguity to
     two entirely different commands, provided that one lies within
     the FTP command space and the other within MP, the two being
     distinguishable by their contexts.  MP and FTP therefore do not
     compete for command names, and MP command names may be chosen
     without regard for the environment in which the subsystem
     resides.
     NOTE:  It so happens that there are commands DEFINED within MP
     which duplicate the functions of FTP commands and bear the same
     names.  The effective result is that some commands are
     explicitly allowed within MP.  The reader will understand that
     this fact is consistent with the conventions described in 1-3
     above, and that no ambiguities result.
  The subsystem concept (if not the name 'subsystem') is taken from
  Mike Padlipsky's Unified User Level Protocol (UULP), which the
  author of the present document strongly supports.  The fact that
  MP is accessed from FTP, rather than both FTP and MP being
  accessed independently from a more general executive program, is
  simply a concession to the fact that FTP is widely implemented and
  UULP isn't.  The author hopes that protocol development will, in
  the near future, begin to proceed along the lines exemplified by
  UULP.




  MP conforms to FTP in general syntax.  In particular, commands and
  their responses are strings of NVT characters; command names are
  limited to four or fewer, upper- or lower-case, alphameric
  characters, and are terminated by the character SP; commands are
  generally terminated with the TELNET New Line sequence (CR LF);
  command responses contain both numeric (process readable) and text
  (human readable) portions.  Both reader and implementer are
  referred to the FTP protocol document for a detailed description
  of such matters; no attempt has been made to duplicate the
  discussion in the present document.
  The FTP protocol document assigns those replies whose second digit
  is '6' to RJE functions.  In like manner MP appropriates those
  reply codes whose second digit is '7' for reporting results
  peculiar to its functions.  It is, however, the author's position
  that FTP, MP, and the RJE protocol are all best implemented as
  subsystems under a common UULP executive, in which case a single
  subset of the reply space could be used unambiguously by all three
  protocols (and any yet to be defined), since every reply would
  implicitly be qualified by the name of the subsystem from which it
  emanates.

THE MAIL MODEL

  MP defines mail to be text communicated between users (both human
  and processes) in less that (but ideally approaching) real time.
  The definition excludes so-called console-to-console
  communication, where users exchange information at the character
  or line level.
  Pieces of mail are characterized by such attributes as title,
  content, author, and recipient.  A piece of mail may be a one- or
  two-line message sent from one individual to another, a draft of a
  document sent by one individual to a design group for review, a
  polished, formal document sent from one group to another, a
  message sent to a human user by a process (e.g., an RJE server
  process might notify a user by Network Mail when his job has
  completed), etc.  All such forms of communication are mail and are
  supported by MP.
  Pieces of mail can be forwarded from one location to another
  Pieces of mail can be replied to.
  The identity of the author of a piece of mail can be verified,
  avoiding forgery and misrepresentation.




  Pieces of mail can be permanently recorded, assigned a long-term
  identifier by which they can be forever be retrieved for
  reference, and entered in catalogs.  And access to such recorded
  mail can be restricted to a specified subset of the user
  community.
  Some hosts accept mail whose recipients reside elsewhere in the
  Network, and assume responsibility for delivering the mail to them
  (worrying about retrying delivery when hosts are down, etc.), and
  acknowledging its delivery to the sender.
  The picture being painted for the reader is one in which processes
  cooperate in various ways to flexibly move and manage Network
  mail.  The author claims (without proof, of course) that the
  picture will in the future get yet more complicated, but that the
  proposal specified here can be conveniently enlarged to handle
  that picture too.

ORGANIZATION OF THIS DOCUMENT

The rest of this document consists of the following components:

  GLOSSARY
     The concepts introduced briefly in the section above are more
     formally defined, and their manner of representation in the
     protocol specified.
  MP FUNCTIONS
     The command sequence is defined by which a user process
     initiates each of the logical functions (e.g., Distribution,
     Recording, Delivery) which can be performed by a Mail server
     process.
  EXAMPLE
     An example of the command-response exchange between a user and
     server is given.
  COMMAND SUMMARY
     A summary of MP commands is given.
  COMMAND REPLIES
     Reply code assignments are given and briefly explained.




  FORMAL SYNTAX
     The formal syntax of the command language is specified.

In all sections but the last (i.e., the formal syntax presentation), verbose keyword forms are employed, in the interests of clarity. These verbose forms have no existence anywhere but in this document; in implementing a Mail user or server process, the terse keyword forms which appear in the formal syntax presentation are to be employed

GLOSSARY

Terms are listed here in alphabetical order. Words or phrases which appear in the definitions with initial letters capitalized are themselves formally defined elsewhere in the glossary.

ACCESS LIST (for a piece of Recorded Mail)

  That set of individuals with access to a piece of Recorded Mail,
  and for each such individual, the type(s) of access granted to
  him.
  An Access List is represented in the Protocol as a series of
  command pairs (juxtaposed in the command stream), each pair
  consisting of an ACCESS command followed immediately (and
  optionally) by an ACCESSTYPES command.  Each pair of commands
  corresponds to one individual in the set.
     ACCESS <individual> <CA>
     ACCESSTYPE <accesstypes> <CA>
        Command arguments identify the Individual to whom access is
        granted, and specify the kind(s) of access allowed him.
        Either Read Access, Controlling Access, or both may be
        granted.
        If no Individual is specified, All is implied.  In the
        absence of an explicit ACCESSTYPES command, one with only
        Read Access specified is to be assumed.
     In the absence of an explicit Access List, one granting Read
     Access to All and Controlling Access to the Author(s) and the
     Clerk is to be assumed.





ACKNOWLEDGMENT (for a piece of Mail)

  A form of Unrecorded Mail, generated by a Distribution Agent,
  whose Recipient is the Monitor for a previous piece of Mail, which
  acknowledges Delivery -- successful or otherwise -- to the
  Recipient(s) of that first piece of Mail.
  An Acknowledgment bears the Serial Number of the Mail it
  acknowledges, as the Reference Serial Number.

ACKNOWLEDGMENT CONDITION (for Acknowledgments)

  The attribute of an Acknowledgment which determines the
  circumstances under which it will be generated by the Distribution
  Agent.
  The following Acknowledgment Conditions are defined:
     ALWAYS
        Acknowledgment is given when all Deliveries are complete,
        regardless of whether or not they are all completed
        successfully.
     FAILURE
        Acknowledgment is given when all Deliveries are complete if
        and only if Delivery to one or more Recipient(s) fails.
     NEVER
        An Acknowledgment is never made.
  An Acknowledgment Condition is represented in the Protocol by the
  command:

ACKCONDITION <ackcondition> <CA>

  In the absence of an explicit ACKCONDITION command, one with an
  argument of FAILURE is to be assumed.

ACKNOWLEDGMENT TYPE (for Acknowledgments and Progress Reports)

  The attribute of an Acknowledgment or Progress Report which
  determines the nature of its Content.





  The following Acknowledgment Types are defined:
     TERSE
        The Content of a TERSE Acknowledgment or Progress Report is
        specified by the Protocol to be an unembellished list of the
        Mail's Recipient(s), and the current Delivery Status for
        each (except that those Recipient(s) whose Delivery Status
        is SUCCESSFUL shall not be included in the list).
        The Content of a TERSE Acknowledgment is one or more
        instances of the following:
           <deliverystatus> <individual> <CRLF>
        TERSE Acknowledgments and Progress Reports are intended to
        be process-readable.
     VERBOSE
        The Content of a VERBOSE Acknowledgment or Progress Report
        is not specified by the Protocol, but might include a list
        of those Recipient(s) to whom the Mail could not be
        delivered and why, the times at which Delivery was made to
        others, etc.
        VERBOSE Acknowledgments and Progress Reports are intended to
        be human-readable.
  An Acknowledgment Type is represented in the Protocol by the
  command:
     ACKTYPE <acktype> <CA>
  In the absence of an explicit ACKTYPE command, one with an
  argument of TERSE is to be assumed.

ALL

  Every conceivable Individual.

AUTHOR (of a piece of Mail)

  An Individual (there may be more than one) given formal
  recognition for having authored a piece of Mail.





AUTHOR LIST (for a piece of Mail)

  That set of Individuals who are Author(s) of a piece of Mail.
  An Author List is represented in the Protocol as an Individual
  List of type AUTHOR.

CATALOG (of Recorded Mail)

  A named data base containing the Citation for each member of a set
  of logically related pieces of Recorded Mail.

CATALOG LIST (for a Piece of Recorded Mail)

  That set of Catalogs which each contain the Citation for a piece
  of Recorded Mail
  A Catalog List is represented in the Protocol as a series of
  instances (juxtaposed in the command stream) of the following
  command.  Each instance corresponds to one Catalog in the set.
     CATALOG <catalog> <CA>

CITATION (for a piece of Recorded Mail)

  The Static and Dynamic Attributes of a piece of Recorded Mail.

CITATION COMPONENT

  Any one of the Static or Dynamic Attributes which comprise a
  Citation.

CITATION RETRIEVAL (for a piece of Recorded Mail)

  The act of retrieving selected Citation Component(s).

CITATION TEMPLATE

  A specified subset of the Citation Component(s) for a piece of
  Recorded Mail.
  A Citation Template is represented in the Protocol by the command:






     CITATIONTEMPLATE <citationtemp> <CA>
  The argument is a list of Citation Component(s).  In the absence
  of an explicit CITATIONTEMPLATE command (or if the argument is
  null), one specifying Content only is to be assumed.

CLERK

  That Individual who prepares a piece of Mail for Recording,
  Distribution, or Delivery.  Conceptually, the Individual with
  proof-reading responsibility for the piece of Mail.
  A Clerk is represented in the Protocol as an Individual List of
  type CLERK and length 1.

COMMENTS (for a piece of Mail)

  An informal, perhaps verbose description of the Content of a piece
  of Mail, or any other information the Author(s) wish to have made
  accessible to the Recipient(s) of the Mail.
  Comments are represented in the Protocol by the command:
     COMMENTS <comments> <CA2>
  In the absence of an explicit COMMENTS command, one with a null
  argument is to be assumed.

CONTENT (of a piece of Mail)

  It's text.
  Content is represented in the protocol by either of the two
  commands below:
     FILE <CA>
        The FILE command implies that the Content of the Mail will
        be transmitted (immediately) as a file using the FTP data
        transfer commands (e.g., BYTE, SOCK, TYPE) currently in
        effect.  FILE is exactly equivalent in use to an FTP STOR
        command (in its use of data transfer commands, in its
        establishment of the data connection, etc.), except that no
        pathname is required, and the server, rather than depositing
        the transmitted file in his file system, disposes of it in a
        manner appropriate for Mail.




     TEXT <string> <CA2>
        The TEXT command implies that the Content of the Mail
        follows on the TELNET connection as a series of lines, each
        delimited from the preceding one by CR LF, and terminated
        finally by a CA2.

CONTROLLING ACCESS (to a piece of Recorded Mail)

  The right of an Individual to modify a Dynamic Attribute of a
  piece of Recorded Mail.
  Recording Agents permit an Individual to modify a Dynamic
  Attribute of a piece of Recorded Mail if and only if he can
  properly identify himself as someone having Controlling Access to
  that Mail.

CREATION DATE (of a piece of Mail)

  The date and time at which the final draft of a piece of Mail is
  completed by the Clerk before he releases it to a Delivery,
  Distribution, or Recording Agent for further processing.  A single
  Creation Date is associated with each piece of Mail.  In general,
  this date is different from the Delivery or Recording Date, since
  Mail often must be queued (for another host to come up) within the
  Delivery, Distribution, or Recording Agent's host before Delivery
  of Recording can occur.
  A Creation Date is represented in the Protocol by the command:
     CREATIONDATE <datetime> <CA>

CUTOFF INTERVAL (for Distribution of a piece of Mail)

  That period of time, measured from the Distribution Date, after
  which the Distribution Agent is to abandon Delivery attempts for
  those Recipient(s) to whom Delivery has not yet been effected.
  A Cutoff Interval is represented in the Protocol by the command:
     CUTOFF <interval> <CA>
  In the absence of an explicit CUTOFF command, one specifying an
  Interval of 7 days is to be assumed.





DELIVERY (of a piece of Mail)

  The act of transmitting a piece of Mail to the host of one of it's
  Recipient(s).

DELIVERY AGENT

  A process which effects Delivery of a piece of Mail.  A
  Distribution Agent is by nature also a Delivery Agent.

DELIVERY DATE (of a piece of Mail to one of its Recipient(s))

  The date and time at which a piece of Mail is Delivered by the
  Delivery Agent to a Recipient's system.  A multitude of Delivery
  Dates, one for each Recipient, are associated with each piece of
  Mail.

DELIVERY STATUS (for a piece of Mail with respect to a Recipient)

  A measure of the extent to which a Delivery Agent has been
  successful, at a given point in time, in Delivering a piece of
  Mail to one of its Recipient(s).  A multitude of Delivery Status',
  one for each Recipient, are associated with each piece of Mail.
  The following Delivery Status' are defined:
     FAILED
        Delivery was rejected by the Recipient's system (e.g., the
        connection request was rejected, the Mail server process
        doesn't support Delivery, the Recipient was not recognized
        by the server).
     SUCCESSFUL
        Delivery was accomplished successfully.
     TIMED OUT
        Either the Recipient's host was disconnected from the Net at
        every Delivery attempt, or no Mail server process has ever
        responded to the connection attempt.  Hope of Delivery has
        been abandoned.






     WAITING
        Either the Recipient's host has been disconnected from the
        Net at every Delivery attempt, or no Mail server process has
        yet responded to the connection attempt.  Delivery attempts
        are continuing periodically.
     UNATTEMPTED
        No delivery attempt has yet been made.

DELIVERY TYPE (for a Delivery)

  The nature of the piece of Mail being delivered.
  The following Delivery Types are defined:
     FORWARD
        A Delivery of type FORWARD represents a piece of Recorded or
        Unrecorded Mail which is being Forwarded.
     MAIL
        A Delivery of type MAIL represents a piece of Recorded or
        Unrecorded Mail whose ultimate source is an Individual.
        This is the "normal" Delivery type.
     NEGATIVE ACKNOWLEDGMENT
        A Delivery of type NEGATIVE ACKNOWLEDGMENT represents a
        piece of Unrecorded Mail generated by a Distribution Agent
        and acknowledging unsuccessful or partially unsuccessful
        Delivery of a previous piece of Mail (identified by
        Reference Serial Number) to it's Recipient(s).  The
        Recipient for this piece of "system" Mail is the Monitor for
        the previous piece of Mail.
     POSITIVE ACKNOWLEDGMENT
        A Delivery of type POSITIVE ACKNOWLEDGMENT represents a
        piece of Unrecorded Mail generated by a Distribution Agent
        and acknowledging successful Delivery of a previous piece of
        Mail (identified by Reference Serial Number) to it's
        Recipient(s).  The Recipient for this piece of "system" Mail
        is the Monitor for the previous piece of Mail.




     PROGRESS REPORT
        A Delivery of type PROGRESS REPORT represents a piece of
        Unrecorded Mail generated by a Distribution Agent and
        reporting the Delivery of a previous piece of Mail
        (identified by Reference Serial Number) to it's
        recipient(s).  The Recipient for this piece of "system" Mail
        is the Monitor for the previous piece of Mail.
     REPLY
        A Delivery of type REPLY represents a piece of Recorded or
        Unrecorded Mail generated in reply (or pertaining) to a
        previous piece of Mail (identified by Reference Serial
        Number).
  Delivery Type is represented in the Protocol by the command:
     DELIVERYTYPE <deliverytype> <CA>
  In the absence of an explicit DELIVERYTYPE command, one with
  argument of MAIL is to be assumed.

DISTRIBUTE DATE (for a piece of Mail)

  The date and time at which a piece of Mail is presented to a
  Distribution Agent for Distribution.

DISTRIBUTION (of a piece of Mail)

  The act of Delivering a piece of Mail to its Recipient(s).
  Distribution can be effected by either the Clerk's Delivery Agent,
  or by a Distribution Agent acting on his behalf.

DISTRIBUTION AGENT

  A Mail server process which acts as intermediary in the delivery
  process by accepting Mail for Recipient(s) in hosts other than its
  own, and then assuming responsibility for Delivering the Mail to
  them and returning Acknowledgment to the appointed Monitor.

DISTRIBUTION LIST

  In the Delivery or Distribution of a piece of Mail, that set of
  Individuals who are to receive Delivery of the Mail.





  In the Recording of Mail, that set of Individuals who have
  received formal and authorized Delivery of a piece of Mail.  The
  list is kept current by Distribution Agents.  Of course, any
  Individual with Read Access to the Mail can himself Deliver it
  informally to anyone he chooses without that fact's being
  reflected in the Distribution list.
  A Distribution List is represented in the Protocol as a series of
  command quintuplets (juxtaposed in the command stream), each
  quintuplet consisting of a RECIPIENT command, followed immediately
  (and optionally) by any or all of the following in the order
  given: a GENERALDELIVERY, a GREETING, a SIGNATURE, and a
  DISPOSITION command.
  Each quintuplet corresponds to one individual in the set.
     RECIPIENT <individual> <CA>
     GENERALDELIVERY <CA>
        This command is appropriate only in the context of the
        Delivery function.  If the previous RECIPIENT command
        illicits the reply:
           474 Recipient unrecognized: is General Delivery
        OK?
        the issuance of the GENERALDELIVERY command constitutes
        consent to proceed with General Delivery to that Recipient.
        If no such consent is given, the RECIPIENT command stands
        rejected.  Unsolicited (i.e., unprompted for) GENERAL
        DELIVERY commands in the Distribution List are treated by
        the server as NOPs.
     GREETING <greeting> <CA>
        The GREETING command specifies the Greeting to be seen by
        the Recipient.
        If the first quintuplet in the list contains no GREETING
        command, one with a null argument is assumed.  Thereafter,
        in the absence of an explicit GREETING command, one
        identical to that for the previous quintuplet is assumed.
     SIGNATURE <signature> <CA>
        The SIGNATURE command specifies the Signature to be seen by
        the Recipient.



        If the first quintuplet in the list contains no SIGNATURE
        command, one with a null argument is assumed.  Thereafter,
        in the absence of an explicit SIGNATURE command, one
        identical to that for the previous quintuplet is assumed.
     DISPOSITION <disposition> <CA>
        The DISPOSITION command identifies the intent with which the
        Mail is Delivered to the Recipient by the Author(s), and may
        take any, all, or none of the following as arguments:
           RSVP
              The Author(s) request a Reply from the Recipient.
           ACTION
              The Author(s) expect some action on the part of the
              Recipient.  If ACTION doesn't appear, then the Mail is
              intended for the Recipient's information only.
           INTERRUPT
              The Author(s) declare that examination of the Mail by
              the Recipient is urgent.  In such cases, the
              Recipient's Mail server process may, upon Delivery,
              choose to interrupt the Recipient if he happens to be
              logged in at a terminal.
        No specific action in response to the presence of any of
        these arguments is required; the server is free if he likes
        to treat DISPOSITION commands as NOPs.
        The absence of a DISPOSITION command implies one with no
        arguments (i.e., for the Recipient's information only, no
        Reply required, and not urgent).

DYNAMIC ATTRIBUTES (of a piece of Recorded Mail)

  Those attributes of a piece of Recorded Mail -- Distribution List,
  Access List, and Catalog List -- which, though given initial
  values at Recording Time, can always be modified by an Individual
  with Controlling Access to the piece of Mail.

FORWARDING (of Mail received for an Individual)

  The act of transferring that set of Mail which has been previously
  Delivered to but not Read by an Individual, to another Individual.



  Users who are known at more than one host can cause their unRead
  Mailto be gathered in to a central location by performing the
  Forwarding function at each such host (both Individuals being, in
  this case, instances of the same User).  Mail which has been
  Forwarded is considered to have been Read at its source.

FORWARDEE

  That Individual whose Delivered but UnRead Mail is to be
  Forwarded.
  A Forwardee is represented in the Protocol as an Individual List
  of type FORWARDEE and length 1.

GENERAL DELIVERY (of a piece of Mail to an unrecognized Recipient)

  The act on the part of a server of accepting Delivery of a piece
  of Mail on behalf of an intended Recipient whose name the server
  doesn't recognize.  The server retains the Recipient's name, and
  makes it and the other information provided by the user process
  available to some competent person, who attempts to make sense of
  the Recipient's name.  If the Recipient is recognized, the Mail is
  'hand' delivered to the appropriate Individual.
  General Delivery of a piece of Mail to one of its intended
  Recipient(s) is performed only after the server informs the user
  process of its intent and receives the user process' consent.  If
  that consent is not given, or if the server doesn't implement
  General Delivery, the server rejects the Delivery attempt for that
  Recipient.
  Consent for General Delivery is represented in the Protocol by the
  command
     GENERALDELIVERY <CA>

GREETING (for the Delivery of a piece of Mail to a Recipient)

  A short greeting to a Recipient of a piece of Mail. 'Dear Dave' is
  a valid and perhaps typical Greeting.
  A Greeting is represented in the Protocol by the command:
     GREETING <greeting> <CA>





ID (for an Individual)

  The password which an Individual may have to present to a Mail
  server process, to prove his identity.
  An Id is represented in the Protocol by the command:
     ID <id> <CA>
  Ids have nothing to do with accounting, and when required by a
  server, they're required only to protect that server from forgery
  or misrepresentation.

INDIVIDUAL

  An instance of a User, identified by NIC Ident, or by the
  combination of host and Mailbox Name.

INDIVIDUAL LIST (of type "t" and length "n")

  A set of Individuals.
  An Individual List is represented in the Protocol as a series of
  "n" command pairs (juxtaposed in the command stream), each pair
  consisting of a "t" command, followed immediately by an ID
  command.  Each pair corresponds to one Individual in the set.
  The ID command is given by the Mail user process at the option of
  the Mail server process; and whenever the server requires it, he
  must prompt for it with an appropriate reply to the preceding "t"
  command.  If no such prompt is given, the user process is not
  obliged to provide the ID command, but may if it chooses, in which
  case the server is obliged to treat it as if it had been prompted
  for and found correct.
  The ID command is a mechanism by which the server can assure
  himself that the user process is not acting without proper
  authorization from the Individual(s) involved, i.e., a mechanism
  by which a server can protect himself against forgery,
  misrepresentation, etc.
     "t" <individual> <CA>
     ID <id> <CA>





MAIL

  A body of text communicated from one set of Individual(s) to
  another, in less than (but ideally approaching) real time.

MAILBOX NAME

  The name a User employs at a host to send and receive Mail.

MONITOR (for a piece of Mail)

  The Individual who is the recipient for Acknowledgments and
  Progress Reports.
  A Monitor is represented in the Protocol as an Individual List of
  type MONITOR and length 1.
  Monitor defaults to the Clerk if not explicitly specified.

PROGRESS REPORT (for a piece of Mail)

  A form of Unrecorded Mail, generated periodically during the
  distribution process by a Distribution Agent, whose Recipient is
  the Monitor for a previous piece of Mail, and whose Content is a
  list of the Recipient(s) and the current Delivery Status for each.
  A Progress Report bears the Serial Number of the Mail whose status
  it reports, as the Reference Serial Number.

PROTOCOL

  The Mail Protocol (MP).

READ (a piece of previously-Delivered Mail)

  The act, on the part of the User, of examining a piece of
  Delivered Mail.

READ ACCESS (to a piece of Recorded Mail)

  The right of an Individual to retrieve the Content of a piece of
  Recorded Mail.
  Recording Agents permit an Individual to retrieve the Content of a
  piece of Recorded Mail if and only if he can properly identify
  himself as someone having Read Access to that Mail.  An Individual
  can retrieve the Citation (except Content) from the Recording
  Agent independently of whether or not he has Read Access to the
  Mail.



READ DATE (of a piece of Mail for one of its Recipient(s))

  The date and time, necessarily following Delivery, at which a
  piece of Mail is Read by a Recipient.  A multitude of Read Dates,
  one for each Recipient, are associated with each piece of Mail.

RECIPIENT (of a piece of Mail)

  An Individual who has or is to receive Delivery of a piece of
  Mail.

RECORDED MAIL

  A piece of Mail whose Citation is available on a long-term
  (indefinite) basis from a Recording Agent.

RECORDING

  The service provided by a Recording Agent.

RECORDING AGENT

  A Mail server process which accepts Mail, permanently Records its
  Citation, and assigns a pathname by which that information can at
  any time be retrieved by an Individual with appropriate access.

RECORDING DATE

  The date and time at which a piece of Mail is presented to a
  Recording Agent for Recording.  A single Recording Date is
  associated with each piece of Recorded Mail.

REFERENCE SERIAL NUMBER (for an Acknowledgment, Progress Report, or

  Reply)
  The Serial Number of the piece of Mail to which an Acknowledgment,
  Progress Report, or Reply refers.
  A Reference Serial Number is represented in the protocol by the
  command:
     REFERENCESERIAL <serialnumber> <CA>
  In the absence of an explicit REFERENCESERIAL command, no Serial
  Number is to be assumed.





REPLY (to a previous piece of Mail)

  A piece of Recorded or Unrecorded Mail whose Author(s) are
  Recipient(s) of a previous piece of Mail, and which replies or
  pertains to that same piece of Mail and bears its Serial Number,
  as the Reference Serial Number.

REPORT INTERVAL (for a Progress Report)

  The interval between Progress Reports.
  A Report Interval is represented in the Protocol by the command:
     REPORTINTERVAL <interval> <CA>
  In the absence of an explicit REPORTINTERVAL command, one with an
  argument whose value is effectively infinite is to be assumed
  (i.e., no Progress Reports are to be made).

REQUESTOR

  The Individual on whose behalf a Mail user process connects to and
  interacts with a Mail server process.
  A Requestor is represented in the Protocol as an Individual List
  of type REQUESTOR and length 1.

SERIAL NUMBER (for a piece of Mail)

  A short-term identifier, assigned to a piece of Mail by the Clerk
  (or his system), which accompanies Acknowledgments, Progress
  Reports, and Replies, and is used to correlate the latter with the
  former.  The lifetime of a Serial Number is conceptually from its
  assignment by the Clerk until the Delivery of the Recipient(s)
  Reply(s) to the Author(s) (or until their decision to send no
  reply).
  A serial Number is represented in the Protocol by the command:
     SERIAL <serialnumber> <CA>
  In the absence of an explicit SERIAL command, no Serial Number is
  to be assumed.

SIGNATURE (for the delivery of a piece of Mail to a Recipient)

  A human-readable indication of the Author(s) of a piece of Mail.
  The string 'Jim and Dick' is a valid Signature.



  A Signature is represented in the Protocol by the command:
     SIGNATURE <signature> <CA>

STATIC ATTRIBUTES (of a piece of Recorded Mail)

  Those attributes of a piece of Recorded Mail -- Content, Title,
  Comments, Author(s), Clerk, and Creation Date -- which are forever
  fixed at Recording Time, and hence can never be modified.
  Static Attributes can be independently specified with commands
  described elsewhere, or specified collectively by reference to an
  existing piece of Recorded Mail.  The command which follows
  assigns to the current piece of Mail the Static Attributes of the
  piece of Recorded Mail it references, and is exactly equivalent to
  an appropriate set of TITLE, COMMENTS, etc.  commands.
     LOCATION <fileaddr> <CA>

TITLE (of a piece of Mail)

  A concise description of the Content of a piece of Mail.
  A Title is represented in the Protocol by the command:
     TITLE <title> <CA>
  In the absence of an explicit TITLE command, one with a null
  argument is to be assumed.

UNRECORDED MAIL

  Mail which is never presented to a Recording Agent for permanent
  storage and cataloging, but which is simply Delivered to its
  Recipient(s) by a Delivery Agent.

UPDATE REQUEST (to a Recording Agent for a piece of Recorded Mail)

  A request made of a Recording Agent to add, replace, or delete an
  Individual from the Access or Distribution List for a piece of
  Mail; or to add or delete a Catalog from the Catalog List.
  An Update Request is represented in the Protocol by the command:
     UPDATETYPE <updatetype> <CA>
  followed immediately in the command stream by an Access,
  Distribution or Catalog List.



USER

  A process or human who sends and/or receives Mail.

USER VERIFICATION

  The act of verifying an ID as that of a specified Individual.

USER VERIFICATION AGENT

  A Mail server process which performs User Verification

MP FUNCTIONS

A MP function is the request by a Mail user process and the subsequent performance by a server, of a major task related to the management of Mail. The following functions are defined:

  RECORDING
  DELIVERY
  DISTRIBUTION
  FORWARDING
  CITATION RETRIEVAL
  UPDATE CITATION
  USER VERIFICATION

One might expect that within the Network there would be just a few Recording Agents (who implement the Recording, Citation Retrieval, and Update Citation functions); a few Distribution Agents (who implement the Distribution function); one or two User Verification Agents (who implement the User Verification Function); and many hosts who implement the Delivery and Forwarding functions.

In general, a host is free to implement any, all, or none of the functions defined by the Protocol; and a host is free to require a login (for purposes of accounting) before permitting a user process access to any of the function(s) it has implemented.

An FTP server process who chooses to not implement MP or a particular MP function simply rejects the command that requests the unimplemented server with the reply:

  400 Function not implemented.

A server who chooses to require login before allowing access to the MP subsystem or to an MP function, simply rejects the command that requests the charged-for service with the reply:




  332 Login first, please.

The functions defined in MP are:

  RECORDING
     The Recording function is invoked with the command:
        RECORD <CA>
     Once this command is given, the user process shall provide the
     following (in any order that suits it):
        (1)   Any Static Attributes desired.
           Content and Clerk are required.  Defaults for other
           Static Attributes (applied by the server if the
           appropriate commands don't appear) are as follows:
              Title or Comments as specified in the glossary.
              Author to the Clerk.
              Creation Date to the Recording Date.
        (2)   Initial values for any Dynamic Attributes desired.
           Defaults (applied by the server if the appropriate
           commands don't appear) are as follows:
              Distribution and Catalog Lists to null.
              Access List as specified in the glossary.
     The Recording function is terminated with either of the
     commands:
        EXIT <CA>    or    ABORT <CA>
     EXIT represents normal termination, and causes the server to
     perform the Recording function for which parameters have just
     been given.  ABORT represents abnormal termination and effects
     exit from the function with no action having been taken by the
     server; the whole command exchange, beginning with RECORD, is
     therefore a NOP.





  DELIVERY
     The Delivery function is invoked with the command:
        DELIVER <CA>
     Once this command is given, the user process shall provide the
     following (in any order that suits it):
        (1)   Any Static Attributes desired.
           Content is required.  Defaults for other Static
           Attributes (applied by the server if the appropriate
           commands don't appear) are as follows:
              Title or Comments as specified in the glossary.
              Clerk to null
              Author to the Clerk.
              Creation Date to the Delivery Date.
        (2)    Any Dynamic Attributes desired.
           Distribution List is required.  Defaults (applied by the
           server if the appropriate commands don't appear) are as
           follows:
              Catalog List to null
              Access List as specified in the glossary.
                 Both of these attributes are for the Recipient's
                 information only when presented in the context of
                 Delivery, so defaulting them to null simply implies
                 that the Clerk doesn't desire that they be
                 communicated to the Recipient.
        (3)   Any or all of the following optional parameters:
           (a) Delivery Type






           (b) Acknowledgment Type
              The specification of this parameter is appropriate if
              and only if the Delivery Type is POSITIVE or NEGATIVE
              ACKNOWLEDGMENT or PROGRESS REPORT.  In this context,
              Acknowledgment Type tells the server how to interpret
              the Content of the Acknowledgment.
           (c) Serial Number
              The Serial Number assigned to the piece of Mail being
              Delivered.  This parameter is inappropriate unless the
              Delivery type is FORWARD (in which case the Serial
              Number is the one preserved from the previous
              Delivery), MAIL, or REPLY.
           (d) Reference Serial Number
              The Serial Number assigned to the piece of Mail to
              which the current piece of Mail is either an
              Acknowledgment, Progress Report, or Reply.  The
              specification of this parameter is therefore
              inappropriate if the Delivery Type is MAIL.
     The Delivery function is terminated with either of the
     commands:
        EXIT <CA>    or    ABORT <CA>
     EXIT represents normal termination, and causes the server to
     perform the Delivery function for which parameters have just
     been given.  ABORT represents abnormal termination and effects
     exit from the function with no action having been taken by the
     server; the whole command exchange, beginning with DELIVER, is
     therefore a NOP.
  DISTRIBUTION
     The Distribution function is invoked with the command:
        DISTRIBUTE <CA>
     Once this command is given, the user process shall provide the
     following (in any order that suits it):
        (1) Any Static Attributes desired.




           Content is required.  Defaults for other Static
           Attributes (applied by the server if the appropriate
           commands don't appear) are as follows:
              Title or Comments as specified in the glossary.
              Clerk to null
              Author to the Clerk.
              Creation Date to the Delivery Date.
        (2) Any Dynamic Attributes desired.
           Distribution List is required.  Defaults (applied by the
           server if the appropriate commands don't appear) are as
           follows:
              Catalog List to null
              Access List as specified in the glossary.
                 Both of these attributes are for the Recipient(s)
                 information only when presented in the context of
                 Distribution, so defaulting them to null simply
                 implies that the Clerk doesn't desire that they be
                 communicated to the Recipient(s).
        (3) Any or all of the following optional parameters:
              (a) Delivery Type
                 MAIL, FORWARD, or REPLY only.
              (b) Serial Number
                 The Serial Number of the Mail being Distributed.
                 The Distribution Agent will relay this Serial
                 Number to each Recipient at Delivery.
              (c) Reference Serial Number
                 The Serial Number of the piece of Mail to which the
                 current piece of Mail is a Reply.  The Distribution
                 Agent will relay this Serial Number to each
                 Recipient at Delivery.  The specification of this
                 parameter is appropriate if and only if the
                 Delivery Type is REPLY.



              (d) Acknowledgment Condition
                 An Acknowledgment is requested from the
                 Distribution Agent if and only if the
                 Acknowledgment Condition is other than NEVER.
              (e) Acknowledgment Type
              (f) Cutoff Interval
              (g) Report Interval
                 Progress Reports are requested from the
                 Distribution Agent if and only if this parameter is
                 specified explicitly.
              (h) Monitor
                 This parameter is ignored unless either an
                 Acknowledgment or Progress Reports (or both) are
                 requested.
        The Distribution function is terminated with either of the
        commands:
           EXIT <CA>    or    ABORT <CA>
        EXIT represents normal termination, and causes the server to
        perform the Distribution function for which parameters have
        just been given.  ABORT represents abnormal termination and
        effects exit from the function with no action having been
        taken by the server; the whole command exchange, beginning
        with DISTRIBUTE, is therefore a NOP.
  FORWARDING
     The Forwarding function is invoked with the command:
        FORWARD <CA>
     Once this command is given, the user process shall provide the
     following (in any order that suits it):
        (1) Forwardee





        (2) Distribution list
           This is the set of Individual(s) to whom the Mail is to
           be Forwarded.
     The Forwarding function is terminated with either of the
     commands:
        EXIT <CA>    or    ABORT <CA>
     EXIT represents normal termination, and causes the server to
     perform the Forwarding function for which parameters have just
     been given.  ABORT represents abnormal termination and effects
     exit from the function with no action having been taken by the
     server; the whole command exchange, beginning with FORWARD, is
     therefore a NOP.
  CITATION RETRIEVAL
     The Citation Retrieval function is invoked with the command:
        RETRIEVE <CA>
     Once this command is given, the user process shall provide the
     following (in any order that suits it):
        (1) The pathname of the piece of Mail whose Citation is to
           be retrieved:
           PATHNAME <pathname> <CA>
        (2) Any or all of the following optional parameters:
           (a) Citation Template
           (b) Requestor
              This parameter is required if and only if Content is
              requested and Read Access happens not to be granted to
              All, in which case the server verifies that the
              Requestor has Read Access to the piece of Mail.
           (c) FILE <CA>
              This command is appropriate if and only if Content is
              requested.  The presence of this command implies that
              the Content of the Mail is to be returned to the user
              process (following the return on the TELNET connection



              of any other Citation Component(s) requested) as a
              file using the FTP data transfer commands (e.g., BYTE,
              SOCK, TYPE) currently in effect.  FILE is exactly
              equivalent in effect to an FTP RETR command (in its
              use of data transfer commands, in its establishment of
              the data connection etc.) except that no pathname is
              required.
              In the absence of a FILE command, Content is returned
              on the TELNET connection like any other Citation
              Component.
              The server returns the Citation Components in the
              order requested by the user process (except that
              Content, if requested as a file, is always returned
              after the 'end of citation' indication), each as a
              reply whose numeric code is 172 and whose text is
              exactly the command normally used to communicate that
              same parameter to the server.  A reply whose numeric
              code is 173 terminates the reply list.
              Title and Content, which (in general) may each contain
              the TELNET New Line sequence (CR LF), are represented
              as continued replies, using the FTP reply continuation
              convention (see the FTP protocol document).  The first
              four characters of each reply line except the first
              and last are blanks inserted by the server which must
              be deleted by the user process to correctly recover
              the value of the Title or Content.
     The Citation Retrieval function is terminated with either of
     the commands:
        EXIT <CA>    or    ABORT <CA>
     EXIT represents normal termination, and causes the server to
     perform the Citation Retrieval function for which parameters
     have just been given.  ABORT represents abnormal termination
     and effects exit from the function with no action having been
     taken by the server; the whole command exchange, beginning with
     RETRIEVE, is therefore a NOP.







  UPDATE CITATION
     The Update Citation function is invoked with the command:
        UPDATE <CA>
     Once this command is given, the user process shall provide the
     following (in any order that suits it):
        (1) Requestor
           This parameter is required unless Controlling Access has
           been granted to All, in which case it is treated as a NOP
           if given.  The server verifies that the Requestor has
           Controlling Access to the piece of Mail.
        (2) One or more Update Requests
     The Update Citation function is terminated with either of the
     commands:
        EXIT <CA>    or    ABORT <CA>
     EXIT represents normal termination, and causes the server to
     perform the Update Citation function for which parameters have
     just been given.  ABORT represents abnormal termination and
     effects exit from the function with no action having been taken
     by the server; the whole command exchange, beginning with
     UPDATE, is therefore a NOP.
  USER VERIFICATION
        The User Verification function is invoked with the command:
           VERIFY <CA>
        Once this command is given, the user process shall specify
        any number of Requestors.
        The server prompts for the Id for each, the user process
        provides it, and the server returns a reply whose numeric
        code is 272 is the Id is correct or 472 otherwise.
     The User Verification function is terminated with either of the
     commands:
        EXIT <CA>    or    ABORT <CA>




EXAMPLE

In the example below, a short message is recorded for public access, and distributed to a single recipient. The user process is assumed already connected to the server.

  Note: This would be the implementation of NIC Journal Submission,
  where the NIC is understood to be both a Recording and
  Distribution Agent.

Replies from the server are in brackets.

  MAIL <CA>
     The Mail system is invoked.
     [261 RE DE DI FW CI UP UV -- supported.]
  REC <CA>
     The Recording function is invoked.
     [200 OK.]
  TITL SMFS Runs on TENEX 1.31 at the NIC <CA>
     A Title is given
     [200 OK.]
  TEXT The NIC came up on TENEX 1.31 on 1-APR. <CRLF> I tried SMFS
  here on the new monitor and it <CRLF> works fine.  I don't
  understand why I had <CRLF> problems running your copy of the code
  at <CRLF> BBN-TENEX.  Are you still unable to reference <CRLF> the
  same archived file from two different <CRLF> TENEXs? <CA2>
     The Content of the message is entered.
     [200 OK.]
  CLER WHITE@SRI-ARC <CR>
     The Clerk is identified as White at SRI-ARC.
     [330 OK.  Now Id, please]
  ID id <CA>
     His Id is supplied.
     [200 OK.]





  EXIT <CA>
     Exit from the Recording function is effected, and the pathname
     '15490' is returned by the Recording Agent for the now Recorded
     Mail.
     [270 15490 -- is assigned as the pathname.]
  DIST <CA>
     The Distribution function is invoked.
     [200 OK.]
  LOC SRI-ARC 15490 <CA>
     The message just recorded is specified for Distribution.
     [200 OK.]
  RECI * DHC <CA>
     The Recipient is specified via NIC Ident to be Dave Crocker at
     UCLA-NMC.
     [200 OK.]
  GREE Dave <CA>
     A Greeting is given.
     [200 OK.]
  DISP R
     A reply is requested.
     [200 OK.]
  SIGN Jim
     The message is signed.
     [200 OK.]
  ACKC A <CA>
     Acknowledgment of the Mail's Delivery is requested whether
     Delivery succeeds or fails..
     [200 OK.]
  ACKT T <CA>
     The Acknowledgment is to be terse.
     [200 OK.]



  CUT 1 D <CA>
     If Delivery hasn't been effected within 24 hours, the attempt
     is to be abandoned (and an Acknowledgment of failure returned).
     The Monitor (to whom the Acknowledgment is sent) is allowed to
     default to the Clerk.
     [200 OK.]
  SERI serial <CA>
     A Serial Number is assigned for purposes of coordinating
     Acknowledgment and Reply.  A desirable implementation of the
     sender's user and server processes is one in which the Serial
     Number is assigned by the user process, rather than by the
     human user himself in such a way that his server process can
     automatically make the association between original Mail, and
     subsequent Acknowledgment and Reply.
     [200 OK.]
  EXIT <CA>
     Exit from the Distribution function is effected.
     [200 OK.]
  EXIT <CA>
     Exit from the Mail subsystem is effected.
     [200 OK.]













COMMAND SUMMARY

Every command requires at least one reply from the server.

THOSE SPECIFIC TO MP

  ABORT <CA>
  ACCESS <individual> <CA>
  ACCESSTYPES <accesstypes> <CA>
  ACKCONDITION <ackcondition> <CA>
  ACKTYPE <acktype> <CA>
  AUTHOR <individual> <CA>
  CATALOG <catalog> <CA>
  CITATIONTEMPLATE <citationtemp> <CA>
  CLERK <individual> <CA>
  COMMENTS <comments> <CA>
  CREATIONDATE <datetime> <CA>
  CUTOFF <interval> <CA>
  DELIVER <CA>
  DELIVERYTYPE <deliverytype> <CA>
  DISPOSITION <disposition> <CA>
  DISTRIBUTE <CA>
  EXIT <CA>
  FILE <CA>
  FORWARD <CA>
  FORWARDEE <individual> <CA>
  GENERALDELIVERY <CA>
  GREETING <greeting> <CA>
  ID <id> <CA>
  LOCATION <fileaddr> <CA>
  MAIL <CA>
  MONITOR <individual> <CA>
  PATHNAME <pathname> <CA>
  RECIPIENT <individual> <CA>
  RECORD <CA>
  REFERENCESERIAL <serialnumber> <CA>
  REPORTINTERVAL <interval> <CA>
  REQUESTOR <individual> <CA>
  RETRIEVE <CA>
  SERIAL <serialnumber> <CA>
  SIGNATURE <signature> <CA>
  TEXT <string> <CA2>
  TITLE <title> <CA>
  UPDATE <CA>
  UPDATETYPE <updatetype> <CA>
  VERIFY <CA>




THOSE BORROWED FROM FTP

  The following commands borrowed from FTP are defined (also) as MP
  commands to support the transfer of the Content of a piece of Mail
  in 'file' form.  The reader is referred to the FTP protocol
  document for a description of their use and syntax.  The borrowed
  commands are:
     BYTE, SOCK, PASV, TYPE, STRU, MODE, REST, and SITE.
  The following commands borrowed from FTP are defined (also) as MP
  commands to permit changes of accounting parameters within the MP
  subsystem.  The accounting parameters in force when the subsystem
  is entered apply (if necessary) within the subsystem until
  changed.  Values to which the parameters may have been changed
  while in the subsystem continue in effect upon return to the FTP
  command space.  The borrowed commands are:
     USER, PASS, and ACCT.
  The following miscellaneous commands borrowed from FTP are defined
  also as MP commands:
     HELP and NOOP.

COMMAND REPLIES

This list is undoubtedly incomplete; some crucial reply code assignments may be missing despite the author's attempt to foresee the kinds of interaction that might arise between user and server and the responses from the server that they would require.

  172 <A Citation Component>
      In response to the EXIT command which terminates the Citation
      Retrieval function.
  173 End of citation.
      Following a list of 172 replies.
  200 OK.
      This is the standard, positive acknowledgment used throughout
      the Protocol.





  270 <pathname> -- is assigned as the pathname.
      In response to the EXIT command which terminates the Record
      function.
  271 <functionlist> -- supported.
      In response to the MAIL command by which the user process
      gains entry to the Mail subsystem.  This response is
      mandatory, and from it the user process can quickly determine
      what function(s) are supported by the server.
  272 Requestor is who he says he is.
      In response to an ID command in the User Verification
      function.  This reply informs the user process that the Id
      given is in fact that of the Individual specified.
  330 OK.  Now Id, please.
      In response to the first command in each pair of commands in
      an Individual List.  This reply requires the next command from
      the user process to be ID.
  332 Login first, please.
      In response to any command which  invokes a Mail function
      (e.g., RECORD, DISTRIBUTE, DELIVER), or to the MAIL command
      itself.  This reply implies that the requested function is
      supported by the server, but that the user is required to
      login before invoking it.
  400 Function not implemented.
      In response to any command which invokes a Mail function
      (e.g., RECORD, DISTRIBUTE, DELIVER), or to the MAIL command
      itself.  This reply implies that the requested function is not
      supported by the server.
  431 Incorrect Id.
      In response to the ID command in an Individual List command
      pair.  This reply implies that the Id specified was incorrect.






  440 <Error relayed from Recording Agent>
      In response to the LOCATION command.  This reply implies that
      the server attempted to retrieve the specified piece of Mail
      from an FTP server but failed because it returned the error
      reply whose text is duplicated in the current reply.
  470 No such pathname.
      In response to the PATHNAME command (in the Citation Retrieval
      function).  This reply implies that the specified pathname is
      not recognized by the server.
  471 No unRead Mail to Forward.
      In response to the EXIT command which terminates the
      Forwarding Function.
  472 Requestor is NOT who he says he is.
      In response to an ID command in the User Verification
      function.  This reply informs the user process that the Id
      given is NOT that of the Individual specified.
  473 You don't have Read Access to the Mail.
      In response to the LOCATION command, or to the PATHNAME
      command in a Citation Retrieval function.  This reply implies
      that the Requestor doesn't have Read Access to the piece of
      Mail.
  474 Recipient unrecognized; is General Delivery OK?
      In response to an instance of the RECIPIENT command in a
      Distribution List (in the context of the Delivery function).
      This response implies that the Recipient in unrecognized, but
      that the server will attempt General Delivery to him if the
      user process responds with a GENERALDELIVERY command;
      otherwise the Recipient is rejected.
  475 That Individual is not at this host.
  570 No such NIC Ident or Mailbox Name.
      In response to any command in which a NIC Ident or Mailbox
      Name appears as an argument.  This reply implies that the
      Individual specified does not exist.




  571 Invalid host.
      In response to any command in which a host address or standard
      host name appears as an argument.  This reply implies that no
      such host exists.
  572 No such catalog.
      In response to the CATALOG command.  This reply implies that
      no such Catalog exists.
  Any '500' reply.

Any of the error replies associated with FTP RETR/STOR commands.

FORMAL SYNTAX

The terse keyword forms to be employed in actually implementing a Mail user or server process are generated by deleting character(s) from the corresponding verbose forms. Those deleted characters are included but enclosed in brackets throughout the description which follows. Spaces can be used freely between terminal elements of the syntax, and in some cases, at least one space must separate two elements whose boundary could not otherwise be distinguished.

<CA2> ::= TELNET Go Ahead character <CA> ::= TELNET new line (CR LF) <CRLF> ::= CR LF <accesstypes> ::= <readaccess> <controlaccess> <ackcondition> ::= A[LWAYS] | F[AILURE] | N[EVER] <acktype> ::= T[ERSE] | V[ERBOSE] <action> ::= A[CTION] | null <catalog> ::= <string> <citationcomp> ::= D[ISTRIBUTION]L[IST] | A[CESS]L[IST] |

                    C[ATALOG]L[IST] | C[ON]T[ENT] |  T[ITLE] |
                    C[OM]M[ENTS] | AU[THOR] | CL[ERK] |
                    C[REATION]D[ATE]

<citationtemp> ::= <citationcomp> | <citationcomp>

                    <citationtemp>

<command> ::= <shortbody> <CA> | <longbody> <CA2> <comments> ::= <string> <controlaccess> ::= C[ONTROLLING] | null <count> ::= decimal integer <date> ::= <dayofmonth> / <month> / <year> <datetime> ::= <date>



                    W[AITING] | U[NATTEMPTED]

<deliverytype> ::= F[ORWARD] | M[AIL] | N[EGATIVE

                    ACKNOWLEDGMENT] | P[OSITIVE
                    ACKNOWLEDGMENT] | P[ROGRESS]R[EPORT]
                    | R[EPLY]

<disposition> ::= <rsvp> <action> <interrupt> <fileaddr> ::= <host> <pathname> <functionlist> ::= <functiontype> | <functiontype>

                    <functionlist>

<functiontype> ::= RE[CORDING] | DE[LIVERY] | DI[STRIBUTION] |

                    F[OR]W[ARDING] | CI[TATION RETEiEVAL] |
                    UP[DATE] | U[SER]V[ERIFICATION]

<globalname> ::= * <nicident> <greeting> ::= <string> <host> ::= <hostname> | <hostaddress> <hostaddress> ::= decimal integer, 0-255 <hostname> ::= standard host name <hour> ::= decimal integer, 0-23 <hours> ::= <count> H[OURS] <individual> ::= <localname> | <globalname> <interrupt> ::= I[NTERRUPT] | null <interval> ::= <days> | <hours> | <days> <hours> <localname> ::= <mailbox> @ <host> | <mailbox> @

  NOTE: Host defaults to that of the server

<longbody> ::= COM[MENTS] <comments> |

                    TEXT <string>

<mailbox> ::= <string> <minute> ::= decimal integer, 0-59 <month> ::= decimal integer, 1-12 <nicident> ::= <string> <id> ::= <string> <pathname> ::= <string> <readaccess> ::= R[EAD] | null <rsvp> ::= R[SVP] | null <serialnumber> ::= <string> <shortbody> ::= ABOR[T] |

                    ACC[ESS] <individual> |
                    ACKC[ONDITION] <ackcondition> |
                    ACKT[YPE] <acktype> |
                    AC[CESS]TY[PES] <accesstypes> |
                    AUTH[OR] <individual> |
                    CAT[ALOG] <catalog> |
                    CLER[K] <individual> |
                    CR[EATION]DA[TE] <datetime> |
                    CUT[OFF] <interval> |
                    C[ITATION]TEM[PLATE] <citationtemp> |
                    DELI[VER] |
                    DE[LIVERY]TY[PE] <delivverytype> |



                    DISP[OSITION] <disposition> |
                    DIST[RIBUTE] |
                    EXIT |
                    FILE |
                    FOR[WARDE]E <individual> |
                    FOR[WARD] |
                    GEN[ERAL]D[ELIVERY] |
                    GREE[TING] <greeting> |
                    ID <ID> |
                    LOC[ATION] <fileaddr> |
                    MAIL |
                    MON[ITOR] <individual> |
                    PATH[NAME] <pathname> |
                    RECI[PIENT] <individual> |
                    REC[ORD] |
                    REQ[UESTO]R <individual> |
                    R[EFERENCE]SER[IAL] <serialnumber> |
                    R[EPORT]INT[ERVAL] <interval> |
                    SERI[AL] <serialnumber> |
                    SIGN[ATURE] <signature> |
                    TITL[E] <title> |
                    UPDA[TE] |
                    UP[DATE]TY[PE] <updatetype> |
                    VER[IFY]

<signature> ::= <string> <string> ::= any non-zero number of visible characters

                    (in particular, CA and CA2 are excluded)

                    PDT | GMT

<title> ::= <string> <updatetype> ::= A[DD] | R[EPLACE] | D[ELETE] <year> ::= full year in decimal (e.g., 1973)



     [ This RFC was put into machine readable form for entry ]
           [ into the online RFC archives by Root 2/98 ]