- Issue may occur if user logged in to more than one computer - It may caused by desktop search engines - Third party add ins - To isolate would suggest running Outlook in safe mode and see if issue can be reproduce the issue - If more than one users is complaining disable TCPChimney on server netsh int ip set chimney disabled Exchange 2003 / 2007 – Error | Event ID 9646 | MAPI Session “/o=CONTOSO/ou=First Admin Group/cn=Recipients/cn=UserAlias” exceeded the maximum of 500 objects of type “objtFolder” http://blogs.technet.com/b/samdrey/archive/2011/03/28/exchange-2003-2007-error-event-id-9646-mapi-session-o-contoso-ou-first-admin-group-cn-recipients-cn-useralias-exceeded-the-maximum-of-500-objects-of-type-objtfolder.aspx How to get rid of 9646 events http://blogs.technet.com/b/jeff_stokes/archive/2008/11/25/how-to-get-rid-of-9646-events.aspx

Hi aha_tom, Any updates?

We are currently running on Exchange 2003 SP1, Exchange 2010 co-exist mode. But all production mailbox is on Exchange 2003. Exchange 2010 is still in trial stage. Recently one of our user (Unfortnately one of our Exectuives!) reported an issue from his Outlook 2010 client. It randomly disconnected from Exchange server. Restart Outlook or reboot PC will not make any difference. His Outlook is in Cached mode, his mailbox on the Exchange 2003 server and is around 4GB. We have since checked on our Exchange 2003 server, and discovered a few MSExchangeIS error event 9646. It indicates the user's mailbox MAPI session exceeded the maximum of 32 objects of type of "session". Close all those sessions with TCPView temporarily fix the issue. However, it occurs again after a few hours. Since that we have tried following fixes: Disabled all unused Outlook Add-ins Remove all other mailboxes include PSTs from his Outlook Move his mailbox to Exchange 2010 then move it back to Exchange 2003 (during the move, 2 corrupted items discovered and removed) None of above seems be able to fix the issue. I have already read the MS doco http://support.microsoft.com/kb/842022, which only mentioned Outlook 2007. One thing I notice is, everytime the user has this issue, he will get a prompt "Allow this website to configure user@contoso.com server settings" https://autodiscover.contoso.com/autodiscover.xml Your account was redirected to this website for settings. You should only allow settings from sources you know and trust"... This puzzles me...

My bad, we are on Exchange 2003 SP2. Instead of spend more time troubleshooting on the client PC, we decided to increase the session limit to 64. It's been couple days. So far all good.

In my experience, this problem can be solved by disable caching of all shared folders in the users Outlook profile. This setting can also be applied with GPO. To disable the caching of all shared folders, follow these steps: On the File tab, click Account Settings in theAccount Settings list. In the Account Settings dialog box, click the E-mailtab and then double-click your Microsoft Exchange Server account. In the Change Account dialog box, click More Settings. In the Microsoft Exchange dialog box, click the Advanced tab. Click to clear the Download shared folders check box. Martina Miskovic

Hi aha_tom, Are you sure you are running Exchange 2003 SP1 coexistence with Exchange 2010? If yes, Exchange 2010 doesn't support the following topologies: Coexistence with Exchange 2000 Server or earlier Coexistence with Exchange 2003 versions prior to SP2 Installing an older version of Exchange into a newly created Exchange 2010 organization Exchange 2003 - Planning Roadmap for Upgrade and Coexistence http://technet.microsoft.com/en-us/library/aa998186.aspx Frank Wang

These are a pain to identify at times. Seems like you can reproduce the issue? Disable ALL add-Ins and test. If user has a mobile device like a BB or uses exch EAS, disable access and test. Can you see if all the mapi sessions are from the same client? Sukh