If you receive:
Event ID: 178
Category: X400 Service
An error occurred while transferring in message because the directory name could not be expanded to an O/R address. An X.400 API Association (XAPIA) unable-to-transfer reason code and unrecognized-OR-name diagnostic code were returned. \[MTA SUBMIT 17 73\] (14)
while synchronizing Exchange and MS Mail, the Directory Synchronization object does not have a valid X.400 address.
To fix the problem, use the Exchange Server Administrator program to select the Exchange Server container. Double-click the Directory Synchronization object, and click the E-mail Addresses tab. Enter a valid X.400 address.
You may want to view the following Knowledge Base articles:
Q96060 - PC DirSync: Directory Synchronization (Dir-Sync).
Q147464 - XFOR: Manual Dirsync with Exchange Server as Dirsync Server.
Q148309 - XFOR: Manual Dir-Sync with Exchange as Dir-Sync Requestor.
Q155104 - Event ID 178 Results if Mailbox has No X.400 Address.