I’m curious what others normally do when an Exchange Server starts having serious issues and mailbox data becomes inaccessible.

If you have a recent backup, that should be the first option. Restoring the affected mailbox or Exchange data from a known-good backup is generally safer than trying random repair methods. It’s also worth checking the Exchange services, database status, available disk space, and event logs first, since sometimes the problem is with the server or configuration rather than the mailbox data itself.

For smaller issues, Exchange’s built-in recovery and repair options can help. Depending on the situation, administrators may use tools such as Eseutil or Exchange Management Shell commands to check database health and perform recovery. But I’d be careful with repair operations because aggressive repairs can potentially result in lost or incomplete mailbox data.

The situation gets harder when there is no recent backup, the Exchange database won’t mount, mailboxes are inaccessible, or the Exchange Server has suffered corruption. In those cases, simply repairing the server may not be enough. You may need an Exchange Server Recovery solution that can scan the available data, preview mailboxes, and recover the required emails and other mailbox items.

For those situations, Free Kernel Exchange Recovery is another option worth checking. It’s an Exchange Recovery Tool designed to recover mailbox data from problematic Exchange environments and lets you preview the recoverable data before deciding what to save. The free version can recover up to 25 items per folder, which is useful for testing the recovery before purchasing anything.
https://www.nucleustechnologies.com/exchange-server-recovery.html