Bizarre delays in mailing list messages

Since the cutover in mailing list servers a few months ago, I've been
noticing that some messages suffer unexpected delivery delays,
particularly on the pgsql-committers list. An example today was that
I pushed two patches to three different branches at approximately 16:39
UTC. Of the resulting six -committers messages, the arrival times
looked like this:

Received: from malur.postgresql.org (malur.postgresql.org [217.196.149.56])
by sss.pgh.pa.us (8.14.5/8.14.5) with ESMTP id q9HGdDxS022945
for <tgl(at)sss(dot)pgh(dot)pa(dot)us>; Wed, 17 Oct 2012 12:39:14 -0400 (EDT)
Received: from malur.postgresql.org (malur.postgresql.org [217.196.149.56])
by sss.pgh.pa.us (8.14.5/8.14.5) with ESMTP id q9HGdf14022979
for <tgl(at)sss(dot)pgh(dot)pa(dot)us>; Wed, 17 Oct 2012 12:39:42 -0400 (EDT)
Received: from malur.postgresql.org (malur.postgresql.org [217.196.149.56])
by sss.pgh.pa.us (8.14.5/8.14.5) with ESMTP id q9HGdvZm022994
for <tgl(at)sss(dot)pgh(dot)pa(dot)us>; Wed, 17 Oct 2012 12:39:58 -0400 (EDT)
Received: from malur.postgresql.org (malur.postgresql.org [217.196.149.56])
by sss.pgh.pa.us (8.14.5/8.14.5) with ESMTP id q9HGkIU9023125
for <tgl(at)sss(dot)pgh(dot)pa(dot)us>; Wed, 17 Oct 2012 12:46:18 -0400 (EDT)
Received: from malur.postgresql.org (malur.postgresql.org [217.196.149.56])
by sss.pgh.pa.us (8.14.5/8.14.5) with ESMTP id q9HH11SO025023
for <tgl(at)sss(dot)pgh(dot)pa(dot)us>; Wed, 17 Oct 2012 13:01:02 -0400 (EDT)
Received: from malur.postgresql.org (malur.postgresql.org [217.196.149.56])
by sss.pgh.pa.us (8.14.5/8.14.5) with ESMTP id q9HHNFDL027425
for <tgl(at)sss(dot)pgh(dot)pa(dot)us>; Wed, 17 Oct 2012 13:23:16 -0400 (EDT)

The next line down in each message shows that it got to
malur.postgresql.org promptly enough, eg for the last one

Received: from localhost ([127.0.0.1] helo=postgresql.org)
by malur.postgresql.org with smtp (Exim 4.72)
(envelope-from <pgsql-committers-owner+M49505=tgl=sss(dot)pgh(dot)pa(dot)us(at)postgresql(dot)org>)
id 1TOWet-0004e8-5n
for tgl(at)sss(dot)pgh(dot)pa(dot)us; Wed, 17 Oct 2012 16:39:51 +0000

so it seems like there is something flaky in malur's mail queuing logic.
I don't mind delays of a few minutes, but when it takes most of an hour
it seems like something must be wrong.

regards, tom lane