I'm using postfix 3.4.14-0+deb10u1 as the MTA on my Debian machine,
with
disable_dns_lookups = yes
relayhost [mail.sonic.net]:587
This has worked fine for many years until on 12/3, without any
changes in my local OS / postfix configuration, it started failing to
deliver mail to the relayhost - which I only found out about 5 days
later when the default maximal_queue_lifetime expired.
The only meaningful messages in the mail logs were
Dec 10 00:01:58 celly postfix/smtp[21050]: warning: relayhost configuration
problem
Dec 10 00:01:58 celly postfix/smtp[21050]: send attr reason = unable to look up
host mail.sonic.net: Name or service not known
I cranked the debug level in master.cf up to 3 '-v's resulting in
lots of log messages, but no more details of *why* it was "unable to
look up". I can nslookup, dig (either A or MX records), telnet to port
587, etc. on mail.sonic.net, so it's not a general system DNS issue.
The postfix FAQ sort of touches on this scenario in FAQs 52 and 53,
but about all I can make of that is that it might be running in a chroot
without the right resolv.conf or other resource to do a name lookup. If
that's true, any ideas on how I can figure out where the chroot is? And
why this behavior would have suddenly started happening, without any
changes in my local configuration (that I initiated, at least, and I
don't have any auto-updates configured)?
Finally, is there any way to crank postfix's verbosity up to a level
where it would actually explain why and/or where it's getting these
errors? It would be nice if it would tell me something about *why* there
is a "relayhost configuration problem", in particular.
I also have a query in to Sonic as to whether anything might have
changed on their end - they are Linux-friendly, and even the front-line
support people tend to be clueful.
Thanks,
Jon Leech
oddh...@sonic.net
