Delivery delay between list server and my ISP

[Gary Johnson <garyjohn@xxxxxxxxxx>]

I've been moving my mail list subscriptions from my work address to a
personal address and have encountered a problem with the delivery of
messages from the mutt-users and mutt-dev lists to my ISP:  they are
consistently delayed by about 20 minutes.  The messages from other lists
to my ISP do not experience this delay and the messages from all lists
including the mutt lists to my work address do not experience this
delay.  There is something unique about the relationship between the
mutt list server and my ISP, but I don't know what it could be.

Here are the relevant headers from a recent message to the mutt-users
list as received at my work address,

    Received: from colonelk.gbnet.net (colonelk.gbnet.net [194.70.126.25]) 
            by aglcosbs02x.cos.agilent.com (Postfix) 
            with SMTP id 9DBCB800ED for <garyjohn@xxxxxxxxxxxxxxx>; 
            Wed,  7 Jan 2009 19:05:04 +0000 (GMT)
    Received: (qmail 4032 invoked by uid 610); 7 Jan 2009 19:04:45 -0000
    Received: (qmail 3988 invoked from network); 7 Jan 2009 19:04:28 -0000
    Received: from dm.gbnet.net (194.70.142.30) by colonelk.gbnet.net with 
SMTP; 
            7 Jan 2009 19:04:28 -0000

Here are the relevant headers from the same message as received at my
ISP.

    Received: from colonelk.gbnet.net [194.70.126.25] by mail.spocom.com with 
SMTP; 
            Wed, 7 Jan 2009 11:25:29 -0800
    Received: (qmail 4032 invoked by uid 610); 7 Jan 2009 19:04:45 -0000
    Received: (qmail 3988 invoked from network); 7 Jan 2009 19:04:28 -0000
    Received: from dm.gbnet.net (194.70.142.30) by colonelk.gbnet.net with 
SMTP; 
            7 Jan 2009 19:04:28 -0000

Does anybody--Steve Kennedy?--know what the issue might be and what
might be done to fix it?  A 20-minute delay makes it difficult to
participate in active discussions.

Regards,
Gary