On Mon, Sep 09, 2013 at 01:42:45PM -0400, Wietse Venema wrote:
> > I think I understand the problem;
> > My server has multiple functions and uses, for various reasons,
> > multiple IP addresses. Postfix cycles through these when sending
> > mail to out.
>
> This is incorrect. The Postfix SMTP client does not choose the
> source IP address unless you configure smtp_bind_address or
> smtp_bind_address6 settings.
Which is to say, that the O/S IP stack chooses a source address
based on whatever algorithms it contains, interface status and the
state of the routing tables.
Postfix can optionaly override this choice, and the OP has already
found the correct solution (assuming that it is impractical to
configure all the machine's IPv6 addresses with suitable PTR
records, ...).
--
Viktor.
