I have a reoccurring problem that I'm trying to wrap my head around. It seems somewhat random as well. The main issue is that it seems as though at random times, my users receive their mail after a long delay. Sometimes as much as a day. The issue is with both emails originating from outside as well as internal emails.
We've also noticed that our exchange connection will randomly drop out. Not too sure if these are related or not. It also seems that it's possible that when the connection drops exchange jumps over to offline mode. Now I can't vouch for what the end user is doing, but it's possibler that:
1. The connection to exchange times out
2. Outlook goes to offline mode
3. End user does not know outlook is in offline mode
4. The connection comes back
5. The user stays in offline mode (potentially until the next restart of outlook)
The items above are just an idea I had as to what could be causing the problem. Sadly, I've never seen it myself - I only get work of the issue when an end user gets a flood of emails they should have previously seen