Exchange 2010 user can't receive any new mail over IMAP

I'm transitioning my users from Exchange 2007 to Exchange 2010, and have encountered an odd error.  I have two users who, after being transferred to the new 2010 Mailbox server, can no longer receive any new mail messages on their IMAP clients (Thunderbird).  Using any IMAP client (They've found the same with iMail and Gmail), they can connect to the Exchange 2010 CAS server and retrieve all of their old e-mails, but any mail that has been sent to them since they were moved over to the new Exchange 2010 Mailbox server does not come through to their IMAP Client.  I know the mailbox itself is still receiving new mails, as it can be checked via their cell phones (ActiveSync) or using the OWA web access client.  

As part of the troubleshooting steps I moved their mailboxes back to my 2007 Mailbox server while leaving them connecting through the 2010 CAS server, and they were able to receive all of their old e-mails and properly receive new ones.  As soon as their mailboxes were moved back to the 2010 MB server they stopped receiving new messages on their IMAP clients.

Here's one of their connections from the log file.  It doesn't seem helpful to me, but maybe it is to someone else:
2010-04-15 16:31:20 POST /owa/ev.owa UA=0&oeh=1&ns=MsgVLV2&ev=LoadFresh;Initial+budget>>Conn:1,AD:$null/$null/0%,CAS:
0%,AB:$null/$null/0%,RPC:$null/$null/0%,FC:$null/0,Hash:59215516 443 <username> Mozilla/5.0+(X11;+U;+Linux+x86_64;+en-US;
+rv: 200 0 0 343

Any suggestions?

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SaakarSenior Technical ConsultantCommented:
Is your Exchange 2010 Server fully patched?? there are a lot of fixes in the Rollups that have been released recently the latest one being Rollup 3
Description of Update Rollup 3 for Microsoft Exchange Server 2010 Release to Manufacturing
TooMuchLinuxAuthor Commented:
I've patched it up to Rollup 2.  I can attempt rollup 3, but it doesn't mention resolving this problem anywhere on its fix list.
SaakarSenior Technical ConsultantCommented:
Well the IIS Logs that you have shared is showing http status code as 200, this means its successful...
share a LDP dump of a working and a non working (Migrated user), did u tried creating a test user on E2K10 and check with the issue.. what I would like to confirm here is; whether its happeinig with only migrated users or is it an issue with new users as well

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