I noticed something a bit odd today that I'm soliciting comment on.
I have an SMTP server running Exim 3.35 (just because that's the Debian
stable version). I have it configured to send outgoing messages to
another SMTP server in the same local network.
I noticed in the log that a message that came from outside my domain and
for a recipient outside my domain got relayed to this 2nd server
(which silently discarded it; that was puzzling too). Relaying like
this, needless to say, shouldn't ever happen, and I hadn't noticed it
happening before.
The problem was, I had:
relay_domains_include_local_mx = true
(which I've since eliminated) in my exim.conf, and this message was
addressed to 'host@???'.
Look at this:
$ dig @ns1.dsl.net domain.com -t MX
;; ANSWER SECTION:
domain.com. 1890 IN MX 10 mail.domain.com.
;; ADDITIONAL SECTION:
mail.domain.com. 1890 IN A 127.0.0.1
That's why my server was seeing its own host as an MX for the
recipient's domain, and thus not refusing the relay.
However, they probably don't get a whole lot of E-mail this way. :-)
Do you see their configuration as:
a) clever
b) an innocent misconfiguration
c) abusive
d) why are you bothering us about this? :-)
