Network Working Group                                         A. Bhushan
Request for Comments: 475                                       MIT-DMCG
NIC: 14919                                                 March 6, 1973


                      FTP AND NETWORK MAIL SYSTEM
	
   This paper describes my understanding of the results of the Network
   Mail System meeting SRI-ARC on February 23, 1973, and the
   implications for FTP (File Transfer Protocol).  There was general
   agreement at the meeting that network mail function should be within
   FTP.

   FTP currently provides two commands for handling mail.  The MAIL
   command allows a user to send mail via the TELNET connection (the
   server collects the mail and determines its end by searching for the
   character sequence "CRLF.CRLF").  The MLFL (mail file) command allows
   a user to send mail via the data connection (requires a user-FTP to
   handle the command but transfer is more efficient as server need not
   search for a special character sequence).  These commands are being
   used to provide network mailing facilities.  Local mail and SNDMSG
   programs have been modified at many sites to include network mailing
   (e.g., USER@HOST at BBN_TENEX and MAIL host user at MIT-DMCG).

   The network mail system should provide a facility whereby users can
   conveniently send messages to other network users who have
   "mailboxes" at one or more hosts.  It is not required that the
   messages or mail be delivered in real-time.  The network mail system
   is not an interactive inter-console communication facility, but it
   may be possible for some sites to deliver "urgent" mail to users in
   real-time (e.g., print mail at user console if user is currently
   logged-in).  The mail system also does not provide a general inter-
   process communication facility, though it may be possible to deliver
   messages to programs which have mailbox addresses.  Inter-process and
   inter-entity communication facilities are very desirable but are
   beyond the scope of the network mail system.

   The concepts of "mailbox" and "mailbox addresses" are central to this
   discussion of network mail system.  A mailbox is a place where the
   mail is stored before a user picks it up.  It may be a file in the
   user's directory or it may be a bin for hard-copy.  The mailbox
   address is the address required by the sender in order to send the
   mail to its destination mailbox.  For users who have an "on-line"
   network mailbox, the mailbox address contains the Host address and
   the user's mailbox identification at that Host.  The mailbox
   identification is that which is required by an FTP-server in order
   that it may put the mail in the desired mailbox.  The terms mailbox
   address will be used to refer to the on-line network mailbox address.

   NETWORK MAIL SYSTEM FUNCTIONS

   The network mail system should provide the following six functions:

   1. CREATING: This refers to the manner in which the user creates or
      composes his message.  The FTP servers do not explicitly provide
      any message editing capability (server's editing conventions may
      be applicable in the case of MAIL command).  Editing conventions
      such as those for character delete and line cancel vary widely
      over the network.  The user is most familiar with his local Host
      conventions and these should be used for network mail editing.
      The user also has access to local editing systems which can be
      used for composing message files.  The message file may then be
      transmitted via the MAIL or MLFL commands (MLFL being preferable).
      The present FTP approach of assuming the creation of messages to
      be sender's responsibility seems adequate.  TIP users if they
      desire editing facilities should use intermediate Hosts for
      creating and sending messages.

   2. LOCATING: How sender determines receivers address.  FTP assumes
      that the sender knows the receivers correct address.  There is no
      published or "on-line" list of mailbox addresses.  There is,
      however, a list of network participants maintained (on-line) and
      published by the Network Information Center (NIC) at SRI-ARC.  The
      network users have been assigned a unique "NIC Ident" and Host
      site by the NIC.  It was therefore specified in FTP that FTP-
      servers maintain a table that maps NIC Idents to mail-box
      identifications.  The NIC will maintain on-line and publish the
      local mailbox address information for network participants.  It
      would be possible for users to look up a published list, or querry
      the NIC on-line to locate destination addresses.  The NIC will
      also provide an on-line facility (similar to FTP) that can be used
      by programs for retrieving the address information.  This latter
      approach of the NIC's maintaining addresses has several
      advantages.  The user can obtain a number of addresses for a
      group, and use these to transmit mail.  The FTP servers need not
      maintain NIC Ident Tables, and the NIC can provide a good facility
      for locating addresses from last names, NIC Idents, or even
      sketchy information.  It may still be desirable that FTP servers
      accept NIC idents, last names, and other standard forms as mailbox
      identifiers.

   3. SENDING: How message is sent to the destination mailbox.  The
      messages may be sent directly to the destination mailbox (via
      TELNET or Data connections) or via an intermediate Host such as
      the NIC.  FTP does not explicitly provide for mail forwarding by
      intermediate Hosts but FTP servers may be able to recognize
      addresses as not being local, and forward mail.  In the event mail

      is to be forwarded, a desirable facility is to have the
      intermediate site return an acknowledgement (by request) upon
      delivery of mail or if delivery fails within a specified time.
      The current FTP specifications recommend that FTP-servers accept
      multiple addresses but do not require this.

   4. STORING: Where mail is stored before reading and if information is
      available for later reference or retrieval.  The FTP does not
      require that sender store mail or keep duplicate copies.  It is
      the receiver's responsibility to store the information for
      reading, reference, or retrieval.  The receiver need not store the
      mail as a data file but can directly print it out on a user
      console or line printer.  FTP does not specify the procedures for
      storage handling by intermediate sites.  If intermediate site is
      used for forwarding the mail until it is delivered to its final
      destination.  If the mail is undeliverable then the intermediate
      site should return the undelivered information to the sender.  A
      similar situation arises when sending of mail is deferred by the
      sending site (destination host may be down).  The sending site
      then acts as an intermediate forwarder insofar as the user is
      concerned.

   5. RECORDING: Should the mail be catalogued and recorded for later
      reference and retrieval.  FTP currently does not provide an
      explicit mechanism for the receiver to record mail.  If an
      intermediate site (the NIC) is used for mail distribution then a
      function of such a site could be to record mail, if so requested.
      NIC is ideal for recording mail, but other sites may also wish to
      record the mail.  If the mail is recorded, then it is not
      necessary to send the entire contents of the mail.  Instead only a
      citation for the document can be sent and the receiver can
      retrieve the mail only if he wants to.  This is particularly
      useful for large documents such as NWG/RFC which are distributed
      to a group.  The citation may contain author, title, retrieval
      pathname, and perhaps an abstract.

   6. READING: How the mail is finally presented to and read by the
      user.  FTP currently assumes that mail reading is entirely the
      receiving site's function.  However, there are ways in which the
      sender can aid the receiver in providing improved mail reading
      facilities.  For example, the receiving system, if it knows a
      message to be urgent can deliver it immediately at a user console.
      Long messages may be put in separate files with notification in
      user's regular mail.  Alternately, mail could be a citation that
      the reading program can retrieve upon user request.  Selective
      handling of different classes of mail is important for an improved
      network mail system.

   MODELS FOR MAIL SYSTEM USE

   The user of a mail system can use intermediate site for locating
   addresses, recording and/or distributing mail, and for creating and
   reading mail.  We therefore have the following models for mail system
   use:

   1. The user connects directly to the destination FTP server and sends
      mail using the MAIL command.  Local editing functions are limited
      to character delete and line cancel (assuming user is in line-at-
      a-time mode) and server conventions may also apply.  The user only
      needs a user-TELNET program at his site but needs to know the
      destination address.  This model is specially applicable to TIP
      and other mini-Host users who do not have a user-FTP or user-Mail
      programs.

   2. The user composes the mail using a local editor (or mail system)
      and then requests his user-FTP or mail program to send the mail
      directly to the destination via the FTP MAIL or MLFL commands.
      The user needs to know the destination address.  The mail can be
      deferred by the sending program if the destination Host is down.
      TIP users can use this model by using the facilities of a "home-
      base" Host.

   3. The user uses an intermediate site such as NIC (other sites may
      provide forwarding services too) for mail distribution.  The user
      need not know the destination addresses but can use NIC idents for
      individuals and groups of individuals.  The mail can be recorded
      on request and its sending can be deferred (the destination Host
      may be down, or it may be more economical to defer mail).  The
      message to be mailed may be created at the local site using local
      editing facilities, or it may be created directly at the
      intermediate site.

   4. The user may send a citation of the mail instead of the complete
      mail item.  The citation refers to an existing document which can
      be retrieved on-line (such as the NIC number of a NIC journal
      communication).

   MAILING TO TIP USERS

   The TIP does not currently provide an FTP server or mailbox
   facilities.  While it is possible to send mail to TIP terminals (such
   as line printers) it seems undesirable to do so because of the
   possibility of losing mail, the lack of privacy, and the fact that
   user may be several (or several hundred) miles away from the location
   of the TIP.  The TIP users normally have a "home-base" computer where
   they do their computing work most of the time.  The TIP user problem

   is best solved by requiring that TIP users rent mailboxes at their
   "home-base" Host.  Such a Host can provide good mail reading and
   querry facilities.  A TIP user can request his "home" Host to send
   him notification of mail on a TIP terminal.  If RDML command (NWG/RFC
   458) is accepted in FTP, TIP users could use such a command.  More
   important, if the user has a number of mailboxes on different Hosts,
   the RDML (or RDMF) command can be used to read his mail at all the
   sites where he has mailboxes.

   ACCESS CONTROL IN MAIL SYSTEM

   It has been suggested that FTP specification should require that mail
   function (for receiving mail) should be "free", i.e., FTP servers
   should not require the user to "login" (send the USER, PASS, and ACCT
   commands).  In the absence of the access control commands the FTP
   server should charge the cost of receiving mail to an overhead or
   browsing account.  It should be noted that this "free" mail function
   using default "USER" account may not allow non mail-related commands
   without reinitializing.  This requirement will improve communication
   among the network users.

   Some systems, such as Multics, have mechanisms for access control in
   the receipt of mail.  That is a user can specify who is eligible to
   send him mail (normally users give then access ".*.*.*.", i.e., any
   one can send mail).  The access control commands would be required to
   gain privileged access.  The USER command does not seem the best way
   to identify the sender of mail.  Consider users logged in as GUEST,
   ICCC, NETWORK, MIT-DMCG, and NETWORK-USER.  A separate FROM command
   seems desirable.  Such a command can be used to identify the sender
   as well as to send acknowledgments and replies.  The receiving site
   can tag the mail as: FROM AKB at MIT-DMCG, logged in as GUEST.  The
   receiver can then send reply to the mailbox address AKB at Host 70
   (SNDMSG AKB@DMCG or MAIL DMCG AKB).

   NETWORK INFORMATION CENTER FUNCTIONS

   The NIC is a very special facility for handling mail.  It provides
   facilities for recording and distributing mail to individuals and
   groups of individuals, and for locating users' addresses.  The NIC
   will also undertake to provide distribution of unrecorded mail.
   Currently the NIC requires that users log into the NIC and use NLS to
   create and distribute mail.  Using NLS for creating mail has been a
   frustrating experience for many who are used to different editing
   systems.  Recently there has been a problem that NIC is overloaded at
   most times of the day and even if one can get a "network terminal"
   and log in, the interaction is quite slow.  As NIC (or NLS) is
   designed for character-at-a-time interaction with remote echo, the

   use is inefficient.  Using NIC is particularly unbearable when the
   user falls behind in his echo by as much as an entire line.

   An alternative to direct use of NIC is to use the NIC via FTP and
   programs at the user's site.  The user can create journal documents
   using his own local editing system and then transfer it to NIC via
   FTP.  The user may have to specify such information as author, title,
   where the acknowledgment should be sent, and journal number if the
   item is to be recorded.  It should also be possible for users to send
   sequential files to NIC and have them restructuredinto NLS form
   without having to do an "input sequential" (a suggestion is to "NLS"
   the file if its name is suffixed with a .NLS).  Alternately it should
   be possible for user's to retrieve journal documents and other
   sequential files without having to do a previous "output sequential".

   The NIC currently delivers mail via hardcopy and/or on-line.  On-line
   currently means that user must log into NIC to see if he has a
   message and read it by "print branch".  The messages are not seen by
   the destination users for several days and many users get their hard
   copy before they have had a chance to examine their on-line NIC mail.
   If the NIC were to deliver mail via FTP to network users, then the
   mail turn-around time will be greatly speeded and the users will not
   have to log into the NIC.  Large documents need not be mailed to the
   user in their entirety but only a citation need be sent.  The NIC
   willhave to collect the information on the mailbox addresses of
   Network participants for delivering mail, especially since it appears
   that many FTP servers are not "respecting" NIC idents.  It is
   recognized that a user may have only one (the most used) of these
   addresses.

   The NIC identification subsystem (currently accessible via NLS only)
   contains information on users (such as affiliation, US Mail address,
   telephone numbers, etc.) and groups (members, etc.).  The on-line
   mailbox address information can be added here.  The NIC will
   undertake to provide a facility whereby the identification subsystem
   can be querried by programs, allowing mailing programs to retrieve
   the addresses automatically.  This facility will be separate from
   FTP.

   FTP MODIFICATIONS

   The FTP currently does not provide explicit facilities for recording
   mail, communicating sender's address, sending program readable
   citations, specifying author and title for documents, requesting
   acknowledgments, and indicating message type (urgent, ordinary, and
   long).  To overcome these deficiencies, we can take any of the
   following approaches:

   1. Kludge the desired features in the pathname syntax of the MAIL and
      MLFL commands, justifying the kludge on the grounds that most of
      the functions are to be used only by the NIC.

   2. Add new commands for the desired functions and alter the MAIL and
      MLFL commands somewhat to recognize the existence of the new
      commands.

   3. Define a new mail command which incorporates the missing functions
      (in the process defining new commands for the desired functions).
      The MAIL and MLFL commands can be used in their present form but
      may be gradually phased out.

   The first approach seems undesirable to me as many of the missing
   functions can be used by other sites as well.  In addition it will be
   easier to write programs to deal with commands rather than a complex
   syntax.  The second and the third approaches are not very different
   from each other.  The third approach seems preferable as it will
   allow existing mail programs to function in their present form.
   Using the third approach consider the following new FTP commands:

   1. MLTO (mail to): The argument is one or more mailbox identifiers
      separated by "," (commas).  It is suggested that if there is no
      argument, the mail should be sent to some responsible user or
      printed on a printer.  This command starts the sequence of
      optional FTP mail related commands described below.  The sequence
      ends with the TEXT, FILE, or CITA (citation) commands.

   2. FROM: The argument is the address of the sender or senders.  It is
      in a standard form that can be interpreted by programs as well as
      human users.  The information is to be used for identifying the
      sender(s), for sending replies, and for sending acknowledgments if
      the receiver is an intermediate forwarding site.

   3. MTYP (mail type): This identifies the type of mail as U (urgent),
      O (ordinary), and L (long).  The receiving system can take the
      appropriate actions from this knowledge.  The default assumption
      is ordinary mail.

   4. RECO (record the mail): The argument if present is the identifying
      information for recording (such as NIC Journal number).  If no
      argument is present the server will assign the recording
      information and send an appropriate reply (real-time or deferred).

   5. AUTH (author): Identifies the author of the document in a form
      acceptable to the server (NIC ident may be required by NIC).

   6. TITL (title): Identifies the title of the document.  The argument
      is an ASCII string ending with the sequence "CRLF.CRLF".

   7. ACKN (acknowledge): Relevant for intermediate forwarding sites.
      Asks the server to send acknowledgment on delivery or if delivery
      fails within a specified time.

   8. TEXT: No arguments.  Starts the transfer of mail over TELNET
      connection in an identical manner as MAIL.

   9. FILE: No arguments.  Starts transfer of mail over the data
      connection in an identical manner as MLFL.

   10. CITA (citation): Argument is the pathname of retrievable file.

   We also need to define new reply codes for handling mail.  Some sites
   have expressed the need for replies such as "send only X bytes of
   mail".  Other replies could specifically request additional commands
   such as USER/PASS/ACCT for privileged mailing, FROM/ACKN for mail
   forwarding, and AUTH/TITL for recorded mail.  Another suggestion that
   may be given consideration is allowing TYPE/BYTE other than A/8 for
   FILE command.  Mailing large files between like machines such as
   PDP-10s is more efficient in I/36.  The RDML and RDMF commands
   proposed by Bressler and Thomas (NWG/RFC 458) also merit
   consideration as they would aid the handling of mail for users who
   have mailboxes at different Hosts.


        [This RFC was put into machine readable form for entry]
     [into the online RFC archives by Kelly Tardif, Viagenie 10/99]