Ryan Rawdon:
> Is this the intended behavior of smtp_address_preference = any?
To ensure that mail does not get stuck for silly reasons, the Postfix
SMTP client chooses the address family randomly IF MORE THAN ONE
IS SUPPORTED.
Background: Postfix will try only a limited number of IP addresses,
and it will make only a limited number of connections. Otherwise,
it would be trivial to D.O.S. the SMTP client with a bazillion DNS
records that point to a blackhole.
Thus, if you require IPv6 always before IPv4, then some sites may
become unreachable, due to temporary or permanent IPv6 outage, that
could have been reached over IPv4.
Wietse
