I took one of my Exchange 2003 databases down this morning for maintenance and after I had the db remounted BES apparently was not redirecting messages for users on that store. I had to restart the dispatcher service to resume service on those mailboxes. 3.6 resumed with no problems following maintenance on the Exchange server. Has anyone else observed this behavior?

Yes, it happens if there are mapi threads open to mailboxes on that store when you bring it down. This issue doesn't seem as prevelant with 4.0 but when I was on 3.6, I just got in the habit bouncing the BES any time an exchange server was bounce or store dismounted to avoid people complaining.