Over here at this blog site I posted about experiencing the following message in the Application event logs:
Mapi session “/o=Corp./ou=company_VA/cn=Recipients/cn=username” exceeded the maximum of 32 objects of type “session”.
Here is Microsoft’s guide to this issue: Microsoft Knowledge Base article 842022 where they recommend upgrading all this 3rd party software to latest versions if you just can’t remove it. In my case, it ultimately boiled down to AIM flooding MAPI network connections as it tried to check for mail etc. Turning off new mail notifications helped a lot. I had two users who needed to have Windows reinstalled since they had other issues and that cleared up all their issues.
Honestly, I think that Exchange is behaving properly, it really was user activity that caused the errors.