Thanks for that explanation. That was my initial understanding (except that I did not know about the 2 minute recycle) and my IT guy said no that the BB polled our corporate server individually. Somehow that didn't seem right.
Now to add to the answer to the OP given by Dubdub, if the RIM server tries three times (15 min apart) and cannot contact your server for some reason (server down, ISP problems, etc.) it will "kick you off" and send you a message that your account is deactivated. If you get one of those call your IT guy and find out what is wrong with the server and once you know that it is reconnected to the net, go into personal e mail set up with your username and password and reactivate your e mail account.
You can also activate it via your https://bis.na.blackberry.com/html?brand=mycingular
(or =yourbrandname-better bookmark it) log in window.
It is not a matter of if this will happen but when. It seems to happen to people in our company when they are overseas (I was in Chile the first time and my manager was in England) so have an overseas access number ready in case you can't access the web. I have had to do it so many times for a variety of reasons, some of which are mentioned above, that I can almost do it in my sleep.