Test-MRSHealth is one of the simplest test cmdlets in Exchange 2010. It checks three things – whether the mailbox replication service is running on the server, whether the service is responding to an RPC ping and whether the replication service is scanning database queues for jobs.
The Exchange Mailbox Replication service runs on all CAS servers. It is responsible for all mailbox moves, import and export requests.
Run Test-MRSHealth to find the status of the replication service.
If you want to check the status for all CAS servers, run Get-ClientAccessServer | Test-MRSHealth