email messages stuck in queue somewhere after WHM 11 autoupdate?

[boatdesign]

Updated whm/cpanel to 11 via stable branch autoupdate. Everything went fine the night of the upgrade but some time on the 21st something went wrong with exim and some mail was stuck in a queue somehow and not delivered. Users noticed reduced mail volumes on the 22nd. Then today I found that some test messages were not making it through from gmail, another external test mail server, etc. I restarted exim using service exim restart from whm and for the "stopping exim" message it showed failed, twice. But OK on starting exim and everything else. Still the test messages didn't come though. Then restarted exim from WHM GUI and now mail messages are trickling in, back from the 21st, a few at a time.

It appears old messages are queued at /var/spool/exim/input or /msglog or /scan and then an alphabetical / numeric subdirectory -- is there any other location messages might be stuck?

Are the messages in /var/spool/exim the messages that are shown in WHM's mail queue manager? Or no? (there were only 24 messages in WHM's mail queue manager, but more than that waiting for delivery from the 21st and 22nd... I'm not yet sure where these "stuck" messages were queued/stuck.)

Any advice on what to look at from here would be appreciated.

(I did reset ACL's to default following the upgrade instruction for the exim.conf)

[boatdesign]

Looking at the message headers from the delayed messages, what do you make of the received time discrepancy? Were these queued somewhere on my server with exim encountering some problem (but still delivering other messages fine and on schedule, and not showing as down in WHM which is set to monitor exim under service management), or are these retries from the remote server?

Delivery-date: Thu, 23 Aug 2007 21:08:00 -0400
Received: from smtpauth04.prod.mesa1.secureserver.net ([64.202.165.95])
by myserver.com with smtp (Exim 4.63)
(envelope-from <sender@email removed for forum post>)
id 1IONeY-0005C1-Pg
for my@emailaddress-removed-for-forum-post; Thu, 23 Aug 2007 21:08:00 -0400
Received: (qmail 20139 invoked from network); 23 Aug 2007 13:54:42 -0000
Received: from unknown (12.2.85.2)
by smtpauth04.prod.mesa1.secureserver.net (64.202.165.95) with ESMTP; 23 Aug 2007 13:54:41 -0000