WHM 11.2.0 cPanel 11.8.0-C16253 CENTOS Enterprise 4.5 i686 - WHM X v3.1.0 Recently some of my users started complaining that they were receiving occasional delivery failures when sending to some users on some domains. I sat with a client yesterday with laptop ready to tail exim_mainlog and watched it all happen. Message 1 fails, while message 2, sent less than a minute later, goes through without any troubles. Code: 2007-08-09 16:57:08 1IJF4H-0003Iv-Pi ** email@example.com <EASTWOOA@trinity-health.org> R=fail_remote_domains: The mail server could not deliver mail to firstname.lastname@example.org. The account or domain may not exist, they may be blacklisted, or missing the proper dns entries. <-snip-> 2007-08-09 16:58:42 1IJF5q-0003KO-EO => email@example.com <EASTWOOA@trinity-health.org> R=lookuphost T=remote_smtp H=nodcmstemf1.trinity-health.org [18.104.22.168] X=TLSv1:AES256-SHA:256 2007-08-09 16:58:42 1IJF5q-0003KO-EO Completed Poking through the exim_mainlog archives, it looks like this is happening erratically to many of my clients. The issue's erratic nature makes me think the issue is outside the server configuration, but the fact that it is happening to many clients sending to many disparate domains (including gmail.com) makes me think the problem is in the server configuration. I am on an AT&T T1 line.