On Thu, Oct 10, 2013 at 02:39:41AM +0200, Dominik George wrote: > > The correct description is: > > > > When both IPv4 and IPv6 support are enabled, the Postfix SMTP > > client, for Postfix versions prior to 2.8, will attempt to > > connect via IPv6 before attempting to use IPv4. Starting > > with 2.8 protocol preference is controlled via the new > > smtp_address_preference parameter. > > That's not the case on two independent systems here. Whether IPv4 or > IPv6 is used is completely random. This:
"The case" is exactly as described. Random by design. This is the intended behaviour of smtp_address_preference = any with a static preference, Postfix may fail deliver mail to a reachable destination, just because enough IPv4 or enough IPv6 addresses are dead. Remember, Postfix tries a limited number of MX addresses per delivery. -- Viktor.