Answer: As you know Microsoft Exchange 2010 uses Database Availability Group (DAG) to replicate mailbox databases between multiple mailbox servers.
In large networks where mailbox servers are spread across different subnet with firewalls in between we need to make sure the DAG replication traffic is allowed on the firewalls.
So remember that by default DAG use TCP port 64327 for replication.
If you would like to use a different port for DAG replication you can modify the DAG port by using the Exchange PowerShell command:
DatabaseAvailabilityGroup – ReplicationPort
Remember to check the Powershell documentation for the full syntax.