Hi All, we are seeing many traffic from our mailbox server being dropped. Typically its the mailbox server using random UDP port trying to connect to Outlook clients. What is the mailbox server trying to do? Our clients mainly use mapi(tcp/ip) to connect to the mailbox server. Should we allow the server to reach out to the clients?

Refer below article to find out ports require for Mailbox server data paths, normally udp doesn't require for MAPI access... Data Path Security Reference http://technet.microsoft.com/en-us/library/bb331973.aspx Amit Tank | MVP Exchange Server | MCITP: EMA | MCSA: M | http://ExchangeShare.WordPress.com

Hi Thanks, yes i have gone through it. But it did not mention anything about mailbox server connecting to client IP directly using random UDP ports. Was just wondering if this is related to cached mode, where the mailbox server is trying to initiatethe client to do a pull?

Hi,Please understand that Outlook clients perform an request to register UDP port for new mail notification.For detailed information, you can refer to the below KB article:http://support.microsoft.com/kb/839226ThanksAllen