[Mailman-Users] Problem Delivering Mail

[David Andrews]

Some of my lists, and some of my users are unable to send mail. The 
users get a message like this:

Subject: Mail delivery failed: returning message to sender

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

   jobs at nfbnet.org
     local delivery failed

Reporting-MTA: dns; host.nfbnet.org

Action: failed
Final-Recipient: rfc822;jobs at nfbnet.org
Status: 5.0.0

Received: from smtp33.relay.iad3a.emailsrvr.com (localhost [127.0.0.1])
	by smtp33.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id D8CA42B83
	for <jobs at nfbnet.org>; Mon, 15 Jan 2018 13:26:18 -0500 (EST)
Received: by smtp33.relay.iad3a.emailsrvr.com (Authenticated sender: 
xxx at yyy.zzzus) with ESMTPSA id A014A5807
	for <jobs at nfbnet.org>; Mon, 15 Jan 2018 13:26:18 -0500 (EST)
Received: from mmlenovo ([UNAVAILABLE]. [173.217.232.59])
	(using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384)
	by 0.0.0.0:465 (trex/5.7.12);
	Mon, 15 Jan 2018 13:26:18 -0500
Received: from smtp64.iad3a.emailsrvr.com ([173.203.187.64]:33780)
	by host.nfbnet.org with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256)
	(Exim 4.89_1)
	

It is on more than one list -- and more than one user.  This is a 
cPanel installation, but I don't know that this is related, and I 
have access to everything.

Thanks for any ideas.

Dave