Admin Beckspaced:
> i had a similar issue a while back ago when switching to new servers.
> the new servers supported the IPv6 protocol and as far as i remember
> IPv6 is always preferred before IPv4.
> my problem was a missing IP reverse DNS entry for the IPv6 address of my
> server. i had an IPv4 reverse DNS setup but this wasn't enough as IPv6
> is always preferred.
FYI, The SMTP client IP address preference is configurable. With
Postfix 2.9 and later the default is "any" (it chooses IPv4 and
IPv6 randomly with equal probability, so that an outage with one
protocol won't prevent mail from going through)).
Wietse
smtp_address_preference (default: any)
The address type ("ipv6", "ipv4" or "any") that the Postfix SMTP client
will try first, when a destination has IPv6 and IPv4 addresses with
equal MX preference. This feature has no effect unless the inet_proto-
cols setting enables both IPv4 and IPv6.
Postfix SMTP client address preference has evolved. With Postfix 2.8
the default is "ipv6"; earlier implementations are hard-coded to prefer
IPv6 over IPv4.
