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
idq9HGdDxS022945for <tgl@sss.pgh.pa.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
idq9HGdf14022979for <tgl@sss.pgh.pa.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
idq9HGdvZm022994for <tgl@sss.pgh.pa.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
idq9HGkIU9023125for <tgl@sss.pgh.pa.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
idq9HH11SO025023for <tgl@sss.pgh.pa.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
idq9HHNFDL027425for <tgl@sss.pgh.pa.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.pgh.pa.us@postgresql.org>)id1TOWet-0004e8-5nfor tgl@sss.pgh.pa.us; Wed, 17 Oct
201216:39:51 +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