SAP changes with regards to Request Handler timeouts
Problems with Request Handler timeouts trying to send large amounts of control messages in rapid succession.
There were some HTTP 503 response codes ("Service unavailable") propagated from Exchange via RH to the SAP J2EE Item Handler. Temporary 503s can happen if Exchange is under high load, and the messages that were being attempted need to be resent. The problem in this case is that the Item Handler in SP2 does not properly handle 503 (and some others) correctly. The Item Handler immediately marks these emails as so called "dead messages" with no retry.
This issue has been addressed in SAP's SP2 Patch1. In SAP's logic they now no longer consider any email as a dead message. SAP will now retry the message if SAP considers that they have run into a timeout issue with the Request Handler or Exchange server.