On Thu, Jul 21, 2011 at 04:27:00PM -0400, Wietse Venema wrote:
> The alternative would require what is called MX piggy-backing, where
> the MTA looks up the MX records for all the recipients of a message,
> and sorts the recipients by the MX IP address (instead of the
> next-hop domain name like Postfix does) before starting email
> delivery. This would have a major impact on delivery performance
> of large mailing lists. And, since qmail did not implement MX
> piggy-backing, I thought I could get away without it in Postfix.
Also, given sufficient congestion, the MX records can be stale by
the time the message is ready for delivery, and there are complications
when the secondary MX for domain A is a primary for domain B, but the
primary for A is down, so we're delivering both via the same MX host,
but did not know this when deciding how to split the envelope.
MX-piggybacking is rather non-trivial, and it is far from clear that
it is sufficiently desirable.
--
Viktor.
