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]
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