I had a customer who had received a meeting invitation, but new copies of his acceptance response were appearing in his Drafts folder several times a minute. This sounds merely annoying, but if enough of these messages build up, it can cause the indexing service on your Exchange server to take 100% of available CPU cycles, and crash the entire server. The database will fail over to another DAG member, and then that server will crash too, if it hasn’t already. We tried deleting the original message, rebooting the client, shutting down all sessions for this mailbox, including mobile devices…nothing seemed to work. He had no Outlook, ActiveSync, EWS, IMAP, or POP clients running, but the message kept multiplying in his Drafts folder.

Well, you know what they say. If at first you don’t succeed, get a bigger hammer. So I disconnected his mailbox, ran Clean-MailboxDatabase, and then reconnected his mailbox to his AD account. This seemed to work for about an hour, but then the runaway draft replication started again.

What do you do when a bigger hammer doesn’t fix it? Get an even BIGGER hammer, of course!

So I exported his mailbox to a PST file (New-MailboxExportRequest -Identity username -FilePath \\server\share\username.pst) and deleted the mailbox. I created a new, clean mailbox for him and waited to see what would happen. Since there was no runaway replicating message, the problem must have been in the data contained in his old mailbox. So I opened the PST file in Outlook, deleted anything he didn’t need, including the Calendar folder (I checked with him first!), and then ran ScanPST against it. That found and repaired 17 errors. Sounded good to me, so I imported the cleaned PST file using New-MailboxImportRequest and watched the mailbox to see what would happen. The import ran for about 20 minutes before the drafts started appearing again.

I let the import finish and, since I couldn’t think of anything better to do, searched his mailbox for any messages containing any reference to this meeting. What do you think I found? Even though I had deleted the meeting from his Calendar, the original meeting request was still in his Inbox. He had probably never even responded to it. I deleted the meeting request and emptied his Deleted Items, and… the draft response stopped replicating.

I still have no idea what was causing this runaway process–ignoring a meeting request shouldn’t automatically generate any kind of draft messages, let alone thousands of them–but I’ll leave the “why” to Microsoft. The customer doesn’t care as long as his email is working.