--On Tuesday, September 02, 2014 14:30 -0400 John R Levine
<johnl(_at_)taugh(_dot_)com> wrote:
Sadly, though it is very late in the process, I failed to
notice this originally, and must belatedly report a
significant issue noted by Wietse Venema. The response code
for rejecting a recipient with a nullmx domain and a sender
with a nullmx domain are reversed in the draft.
Since 521 like 221 and 421 leads to connection drop after the
reply,
Only when it's the SMTP greeting. In this case it's not.
That suggests that JCK's suggestion to have a new RFC to
replace 1846 is a good one, since it could mention this other
fairly obvious use case.
See draft-klensin-smtp-521code. If additional text is needed
there, please suggest some.
it is only appropriate when the entire envelope will be
rejected. Thus 521 goes with rejection of a nullmx sender
domain and 550 with a particular nullmx recipient.
No, 550 to reject the MAIL FROM is correct. See RFC 5321, sec
3.3. It's a policy rejection.
Yes, or 554, see Section 3 of draft-klensin-smtp-521code for
discussion (and, if I got that wrong, this would be a good time
to discuss it).
john