Re: Clarification of MX lookups when requeuing deferred messages
- On Wed, Nov 14, 2012 at 03:03:00PM +0000, Quinton Phil P wrote:
> I'm after some clarification on how Postfix handles MX lookupsPostfix treats deferred messages in the same way as new messages.
> against domains when you requeue a message that has been deferred.
The queue file does not store any DNS lookup state.
> You take a look at the message and you find it attempted to relayBe more specific. What are the MX records for the destination
> via postfixserver22.bigorg.com.
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 usesThis is false. Is the server in question directly listed in the
> the destination server it found in the first attempt, in this case
destination MX records, or is the site using a load-balancer?
Is the load-balancer if any "sticky" with respect to the client
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.