So basically it's the Meeting Acceptance email he's getting on his Blackberry.
They should be coming to Lotus Notes, but he just doesn't normally see them.
Ask your Domino guys to do a All Document View on his mail file (this will list hidden & mail moved to folders) & you should see the meeting acceptances there.
Is it possible that he's got a rule in Lotus Notes which moves these Meeting Acceptances to another folder?
If so, he may have changed his "Hide Filed Messages" to No (under Messages-> Options, General Options).
Or if not, they're probably automatically Hidden From View. (which is possible, but I can't remember how) (
BlackBerry Search Results &
BlackBerry Search Results )
Finally have your BES guys upgraded their server, or his mail file was moved servers, or soemthing, or did it just start happening?