Network Working Group M. A. Padlipsky
Request for Comments:
491 MIT-Multics
NIC:
15356 12 April 1973
What Is Free
In at least three of the RFC's about "mail" and the File Transfer
Protocol (RFC's 454,
475,
479), something very like the following is
asserted: "Network mail should be free; i.e., no login or USER
command should be required." Unfortunately, "i.e" (=that is) is
misleading. It simply does not follow to imply that the only way
mail can be free is for it not to require a login; explicit login on
a free account would of course also work. Indeed, depending upon
per-Host idiosyncrasies in the Logger / Answering Service / process
creation environment, an explicit login may well prove to be far more
natural than an implicit login. (Even in environments where implicit
login is easy, surely explicit login is just easy.) Granted, login
on a free account requires users to remember the name of the free
account. However, this would not be too great a burden to bear if
there were reasons for preferring an explicit login and if the free
account had the same name on all Hosts. Therefore, from the promise
that Network protocols should not implicitly legislate "unnatural"
implementations for participating Hosts if it is conveniently
avoidable, I propose the following formulation:
Network mail should be free. Network mail should not require
users to remember the name of the free account on a given system.
I.e., it should either be "loginless" or it should take the same
login everywhere. But some systems need/want/prefer a login.
Therefore, USER NETML / PASS NETML should be made to work
everywhere for free mail.
Note: "NETML" is fewer than six characters and is upper case
hence, it should fit in the least common denominator category
of user identifiers, but it's still long enough not to conflict
with anybody's initials (in all probability).
Now, because of the implementation implications this may all sound
like special pleading, but I claim that another implication of the
"incorrect" formulation will further show the superiority of an
explicit login for mail. For the "loginless" view leads to problems
in regard to the authentication aspects of login and the accounting
aspects, by apparently assuming that the sole purpose of login is to
initiate accounting. In
RFC 475, the problem is exposed when, after
noting that some systems allow access control to be applied to
mailboxes, it is asserted that FTP USER command is wrong for access
control because you'd then be on the free account and a new FTP FROM
command would be right. (Presumably, FROM would be followed by
PASS.) Being reasonably familiar with one of the systems which does
allow access control on mailboxes, let me point out how it works:
permissible "principal identifiers" are placed on the "access control
list" of the mailbox, and when the mailbox is referenced by a process
the principal identifier of that process must match (explicitly or as
a member of a class) an entry on the list or access will be
forbidden. But the principal identifier is associated with the
process at login. Now, it is probably a valid objection to say that
accounting should be separated from authentification, but it isn't
always. So why invent a redundant mechanism based on the assumption
that it is?
Another point on authentication via login: it has been argued that
FTP mail ought to be so cheap that it "can be buried in overhead" by
the same token, if it's so cheap it shouldn't bother anybody to login
on his own account if he wants to prove the mail's from himself.
To be scrupulous, I should close by mentioning the possibility that
NETML might be repugnant to some Hosts. If such be the case, then I
propose that a new FTP FREE command be introduced so that Servers
need not recognize MAIL as an implicit login. The reasons here are
at least twofold: First, it appears that when the "subcommands" to
MAIL get worked out, some of them will have to precede the MAIL (or
users will set awfully tired of typing their names, etc.); therefore,
the list of commands which imply a login grow and grow and Server
FTP's will have to change and change. Second, if MAIL implies a
login, it will be hard in some environments to get the arguments
across to the process created on behalf of the mailer (and it is not
a good idea at all to assume that the mailing can be handled by the
process which is listening on socket 3). Even introducing a new
mechanism (and see
RFC 451 for my strong feelings against that sort
of step in general) in FREE seems better than making all the
assumptions that the loginless alternative does.
Note that an alternative to this whole line of reasoning would be
simply to observe that the FTP is internally inconsistent in that it
acknowledges on the one hand (in the definition of the USER command)
that some systems may require USER / PASS and then (mis)states on the
other hand (in the discussion of mail) that they may not. If this
abstract point is more satisfying to some readers than the foregoing
pragmatic argument, well and good.
[This RFC was put into machine readable form for entry]
[into the online RFC archives by Helene Morin, Via Genie,12/1999]