tobs...@brain-force.ch:
> in main.cf
>
> smtp_address_preference = ipv4
> inet_protocols=all
>
> which should ensure postfix client prefers ipv4 over ipv6
Actually, this means try to make connections over IPv4 BEFORE trying
to make connections over IPv6.
> But now we have a mail where we can see that postfix client did AAAA
> lookup. Although the is a valid A record
Except that DNS lookups can fail temporarily, for all kinds of
reasons. This is why network software must be prepared to retry
whan it receives no reply.
> > Dec 29 07:43:34 10.1.0.201 postfix/smtp[38913]: 4JP20t6xYdz3VMH:
> to=<REDACTED>, relay=none, delay=7.5, delays=1.2/0/6.3/0, dsn=4.4.3,
> status=deferred (Host or domain name not found. Name service error for
> name=REDACTED.mail.protection.outlook.com type=AAAA: Host not found,
> try again)
The Postfix queue manager sent a delivery request for the message
with queue ID 4JP20t6xYdz3VMH, which was handled by the Postfix
SMTP client process 38913.
The Postfix SMTP client tried to look up A records for
REDACTED.mail.protection.outlook.com, which failed, then it tried
to look up AAAA records, which also failed. Presumably there was a
brief DNS or network outage or overload somewhere.
The logfile record shows only the result of the last DNS lookup
failure (AAAA lookup). Other feailures may have been logged by the
same SMTP process 38913, but without the 4JP20t6xYdz3VMH queue ID.
(Why didn't the Postfix SMTP client log EVERY failed attempt with
the 4JP20t6xYdz3VMH queue ID? Because the Postfix SMTP client
recovers immediately from many delivery errors by trying a different
DNS lookup, MX host or IP address. When an error is immediately
recoverable, then that is less interesting. That is why Postfix
logs only the errors that aren't immediately recoverable with the
queue ID.)
> According to log it took postfix over 2min to "fallback" to ipv4
>
> > Dec 29 07:46:04 10.1.0.201 postfix/smtp[60301]: 4JP20t6xYdz3VMH:
> to=<REDACTED>,
Two minutes later, the Postfix queue manager sent a DIFFERENT
delivery request for the message with queue ID 4JP20t6xYdz3VMH.
This request was handled by a DIFFERENT Postfix SMTP client process
60301. When that DIFFERFENT process looked up A records, the lookups
succeeded.
Wietse
