Dirk St?cker:
> Hello,
>
> I searched the net but didn't find the a description so I ask here. I'm
> operating two mail servers with postfix and I see that the servers always
> switch between IPv4 and IPv6 when sending mails from one to the other.
>
> Is there a mechanism in postfix to switch randomly between the IP
> addresses of a target server if it has more than one IP?
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".
Postfix always randomizes the order of IP addresses with the same
MX preference (this is so that mail performance won't suck too much
just because one IP address does not work well).
With "smtp_address_preference = any", this random sort mixes IPv6
and IPv6 addresses with the same MX preference. Otherwise, an IPv4
address sorts before or after an IPv6 address with the same MX
preference.
Wietse
