Question : Exchange 2010 mapidelivery queue holding email

Currently have Exchange 2007 which is working fine and we are in the final stages of testing exchange 2010, but can’t get past this intermittent issue of email randomly getting stuck in the mapi delivery queue. Restarting the transport service flushes the queue and it may not occur again for 24 hours plus.
Primary Site Exchange 2010 is setup as follows two client access\hub transport servers setup in a Client access array using NLB. (Outlook Anywhere On) 1 Mailbox server (In DAG) and 1 Unified Comms Server

Secondary Site 1 Client Access\Hub Transport 1 Mailbox Server as the passive member of the DAG

All Hardware far exceeds minimum specs.

Answer : Exchange 2010 mapidelivery queue holding email

Thanks for your help, this has now been resolved. Was a miss configuration by our Network Engineer on the Cisck Firewall.