Bounce warning from ezmlm mailing lists ....

Ezmlm community:

We have been seeing an increase in the number of bounce warning messages 
on some of our ezmlm mailing lists.  While I've been led to believe that 
this may be due to a mis-configured mail delivery system on another host 
I don't seem to be bright enough to figure out what is causing this and 
how to deal with it.  All of our mail, however, I believe is required to 
go from our host to a central SMPT delivery machine.  As near as I can 
tell, we get these bounce warnings on messages send to the individuals 
on the mailing list despite the fact that the message seemed to have 
been successfully delivered.

Can anyone point me in the direction of information that would help to 
sort this out?  Or things that I can look for in the maillog files that 
might help me to sort this out?

Following is the content of one of these messages .... with various 
names sanitized ... including the full header information that it contains.

Thanks for your consideration and inputs,

John

 From [email protected]  Fri Sep 26 15:57:17 2008
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Hi! This is the ezmlm program. I'm managing the
[email protected] mailing list.

I'm working for my owner, who can be reached
at [email protected].


Messages to you from the the-list mailing list seem to
have been bouncing. I've attached a copy of the first bounce
message I received.

If this message bounces too, I will send you a probe. If the probe bounces,
I will remove your address from the the-list mailing list,
without further notice.


I've kept a list of which messages from the the-list mailing list have 
bounced from your address.

Copies of these messages may be in the archive.

To retrieve a set of messages 123-145 (a maximum of 100 per request),
send an empty message to:
   <[email protected]>

To receive a subject and author list for the last 100 or so messages,
send an empty message to:
   <[email protected]>

Here are the message numbers:

   426

--- Enclosed is a copy of the bounce message I received.

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	id 66AEE60E8BE; Thu, 11 Sep 2008 22:01:09 -0700 (PDT)
Date: Thu, 11 Sep 2008 22:01:09 -0700 (PDT)
From: [email protected] (Mail Delivery System)
Subject: Undelivered Mail Returned to Sender
To: the-list-return-426-shott=host.university.edu@host.university.edu
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Message-Id: <[email protected]>