Josef Karliak:
> Hi there,
> just a little question - when I use in the main.cf dns name for
> relayhost and dns name has IPv4 and IPv6 IP, how does postfix
> communicate ? First is IPv6 communication and after timeout is IPv4
> communication ?
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. With Postfix 2.8 the default
is "ipv6".
Notes for mail delivery between sites that have both IPv4 and IPv6 con-
nectivity:
o The setting "smtp_address_preference = ipv6" is unsafe. It can
fail to deliver mail when there is an outage that affects IPv6,
while the destination is still reachable over IPv4.
o The setting "smtp_address_preference = any" is safe. With this,
mail will eventually be delivered even if there is an outage
that affects IPv6 or IPv4, as long as it does not affect both.
This feature is available in Postfix 2.8 and later.
