Cached Exchange Mode Fault Tolerance

Microsoft created Cached Exchange Mode so that users can access an offline copy of their mailbox even when they're disconnected from the Exchange server or the server is down or unavailable. Although users can’t send and receive mail, they can compose messages for future delivery, and they can read all messages that were copied to the cache prior to being disconnected. Sometimes, Cached Exchange Mode might be your only line of defense against system failures.

Any good administrator will tell you that you should always back up your system, test your backups, and have enough redundancy in place to prevent catastrophic failures from disrupting mail flow. In the real world though, these best practices aren’t always followed. Budget cuts and lack of training sometimes lead to subpar Exchange Server deployments.

I once received a call from a client whose Exchange server had catastrophically failed. I discovered that the hard disk containing the database had died, and it was in such bad shape that the data was unrecoverable. The Exchange server had never been backed up. . . .