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RFC 524 - Proposed Mail Protocol


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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> <time>
   <dayofmonth>     ::= decimal integer, 1-31
   <days>           ::= <count> D[AYS]
   <deliverystatus> ::= F[AILED] | S[UCCESSFUL] | T[IMED OUT] |

                        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)
   <time>           ::= <hour> : <minute> <timezone>
   <timezone>       ::= EST | EDT | CST | CDT | MST | MDT | PST |
                        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 ]

 

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