--On Tuesday, July 18, 2000 2:32 PM -0400
Valdis(_dot_)Kletnieks(_at_)vt(_dot_)edu
wrote:
(Am cc'ing the IETF-SMTP list, hopefully it's alive and
somebody there will have guidance on this... For the IETF-SMTP
list, the discussion is what to properly do if handed this
during an SMTP transaction:
MAIL FROM:<user(_at_)domain(_dot_)name@other.domain>
Sendmail currently issues a '250 OK'.
... [more of original message below]...
Hi.
If my memory is correct, 501 (syntax error) is intended, as was
the exclusion of 553 from the MAIL FROM responses. I agree that
the 1123 text is a little muddy (and it is probably at least
partially my fault). Please take a look at
draft-ietf-drums-smtpupd-12.txt and see if you think it is clear
and good enough; if not, comments should probably go to the DRUMS
list (copied on this response).
I would think that 553 would be used for a situation in which,
e.g., the left-hand-side (local-part) of an address was valid
syntax in 821 (etc) terms, but invalid for processing/ delivery
on the target host while 501 would be used for things that were
lexically unacceptable given the 821 grammar. If that were the
theory, then a receiving SMTP wouldn't be able to comment on the
sender's local part (in MAIL FROM) as long as it obeyed the 821
syntax. But, again, a receiving host could evaluate a local-part
syntax against its own rules.
For example, assume my host receives
RCPT TO:<bogus\ user(_at_)my(_dot_)domain>
Almost no one has mailbox names that look like that, so bouncing
it with a 553 would be reasonable. Bouncing it with 501 would be
less so, since the syntax, is I believe, 821-valid. On the
other hand, the example given below is invalid everywhere in 821
systems.
john
On Tue, 18 Jul 2000 10:46:13 PDT, Kyle Jones
<kyle_jones(_at_)wonderworks(_dot_)com> said:
The attitude I took when I ran a relaying server was that stuff
like a(_at_)b@c was better off bounced immediately.
I can deal with that attitude.
However, RFC821 also lists the following codes on page 56:
550 Requested action not taken: mailbox unavailable
[E.g., mailbox not found, no access]
551 User not local; please try <forward-path>
552 Requested mail action aborted: exceeded storage
allocation 553 Requested action not taken: mailbox
name not allowed [E.g., mailbox syntax incorrect]
554 Transaction failed
But then continues to say:
MAIL
S: 250
F: 552, 451, 452
E: 500, 501, 421
RCPT
S: 250, 251
F: 550, 551, 552, 553, 450, 451, 452
E: 500, 501, 503, 421
(I.e. you can toss a 553 on the RCPT TO, but not on a MAIL
FROM).
RFC1123 then muddies things up more:
5.2.10 SMTP Replies: RFC-821 Section 4.2
A receiver-SMTP SHOULD send only the reply codes
listed in section 4.2.2 of RFC-821 or in this
document. A receiver-SMTP SHOULD use the text shown
in examples in RFC-821 whenever appropriate.
A sender-SMTP MUST determine its actions only by the
reply code, not by the text (except for 251 and 551
replies); any text, including no text at all, must be
acceptable. The space (blank) following the reply
code is considered part of the text. Whenever
possible, a sender-SMTP SHOULD test only the first
digit of the reply code, as specified in Appendix E of
RFC-821.
DISCUSSION:
Interoperability problems have arisen with SMTP
systems using reply codes that are not listed
explicitly in RFC- 821 Section 4.3 but are legal
according to the theory of reply codes explained
in Appendix E.
So, is it legal/permissible/suggested to 553 on a MAIL FROM
that can be determined to be syntactically invalid?
--
Valdis Kletnieks
Operating Systems Analyst
Virginia Tech