MX pref 0 rejected?
(too old to reply)
Steven P Vallière
2012-07-20 18:06:10 UTC
I've noticed a fair number of messages list the one below
in my mail logs:

Jul 20 09:52:17 mail postfix/smtpd[2352]: NOQUEUE: reject: RCPT from
unknown[ww.xx.yy.zz]: 450 4.1.8 <***@host.xxxxxxxx.com>: Sender
address rejected: Domain not found; from=<***@host.xxxxxxxx.comm>
to=<***@example.com> proto=ESMTP helo=<host.xxxxxxxx.com>

When these messages were generated, I had reject_unknown_sender_domain
included in my list of smtpd_sender_restrictions. That particular
reject option is supposed to "reject sender from domain without A or
MX record."

Unfortunately, when I went to check on one of the domains (because a
message I was expecting kept being rejected) I discovered that the IP
address logged had both an MX and an A record. Except for the obvious
(IP and name) the records were the same as those for systems whose mail
was being accepted. EXCEPT, the MX preference value is 0 (ZERO) for
the domain whose mail is being rejected.

For now, I removed the reject_unknown_sender_domain setting and I'm
finally receiving the expected messages, but I'd like to know if this
is a known bug and if not, what I can do to help confirm it.

(As you can see, I didn't put the actual names or IP addresses here,
but I'll share them directly with a developer if asked.)

Steve Vallière