Hi misc@opensmtpd.org,
I’ve been a very happy user of OpenSMTPD for some time now, but I encountered a
DNS issue today which seems to have caused mail to be lost.
For some reason, the primary DNS server in the data centre I'm using started
replying to lookups with REFUSED last night. As a result, smtpd couldn't
resolve destination MX addresses and emails stopped getting delivered. Many
/var/log/maillog entries started appearing along the lines of:
smtp-out: routing: Failed to resolve MX for [blah]: Invalid domain name
smtp-out: session 0000000000000000: evpid=blah, status=PermFail, from=<>,
to=<f...@bar.com>, rcpt=<->, source=-, relay=bar.com, delay=0s, stat=Invalid
domain name
warn: queue: no return path!
What surprised me about this situation was that smtpd seems to think it
successfully delivered all those messages. `smtpctl show queue` is empty and
there are no files sitting in /var/spool/smtpd, so as far as I can tell the
messages are gone. I was expecting to find them tucked away in a directory
somewhere waiting for something to be done about them. Is this expected
behaviour?
The other surprising thing to me was that the system's DNS lookups weren't
clever enough to ignore the server that was returning REFUSED and fall back to
the second DNS server listed in /etc/resolv.conf, which was still working just
fine. That's a question for a different list though.
OS and software versions:
FreeBSD 10.3
opensmtpd-5.7.3_2,1
libasr-1.0.2
libevent2-2.0.22_1
Cheers,
Sam
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