I finished the server OS update a few days ago, and all seemed to be going well. I had a few tests to perform, but got distracted away from the keyboard. Yesterday I noticed my e-mail was a little thin, so I thought to spend a few minutes checking things today.
The various web, application, and database servers are all running as expected. The mail server's been running, and with the removed and reinstalled efforts so is the anti-spam server. It seemed that while the mail server was taking in mail, it wasn't taking it in right.
A peek at the sendmail settings showed me where I went wrong, though. The sendmail configuration file had been saved during the upgrade, but wasn't automatically applied. A quick rebuild of the M4 file and restarting the server, and a flurry of mail has come through. I did check and see the file was there after the update, but I didn't send myself messages to ensure the relays worked. Thirty seconds of double-checking and now it seems the only thing that isn't back to normal is the remote desktop, which I don't use that much anyway; I think that's related to the XFCE instead of the regular desktop. It'll probably be just a matter of finding the right setting or adding the right bit of accessory software.