On Wed, Nov 14, 2012 at 03:03:00PM +0000, Quinton Phil P wrote:
> I'm after some clarification on how Postfix handles MX lookups
> against domains when you requeue a message that has been deferred.
Postfix treats deferred messages in the same way as new messages.
The queue file does not store any DNS lookup state.
> You take a look at the message and you find it attempted to relay
> via postfixserver22.bigorg.com.
Be more specific. What are the MX records for the destination
domain? How many hosts are listed, and how many IP addresses per
host? What are the MX preferences?
> Postfix does not do a fresh lookup against bigorg.com, it uses
> the destination server it found in the first attempt, in this case
> postfixserver22.bigorg.com.
This is false. Is the server in question directly listed in the
destination MX records, or is the site using a load-balancer?
Is the load-balancer if any "sticky" with respect to the client
IP address?
Also, if your server delivers a "trickle" of mail to the destination
in question, that is, a steady stream of messages that are sent
approximately once a second, and there is backlog of messages for
the destination in the active queue, the connection cache may
trigger re-use of one active SMTP connection for ~300s before a
new connection is opened. This is most likely if you've configured
a rate limit of ~1 msg/sec to the destination, but are in fact
sending large bursts of mail there.
I don't recall whether enabling rate limits for a transport
disables connection caching for that transport.
--
Viktor.
