While in OWA, we can see the emails coming into inbox, however after several seconds they disappear so that users never see them in their Outlook inboxes. This happens occasionaly for some messages and they are neither in Junk mail nor in Deleted messages folders. They just disappear.
We've checked rules in Outlook, junk mail settings. Also, all messages are delivered to exchange mailboxes, not to .pst files.
At the same time, we've got BlackBerry enterprise server, that is delivering emails to BlackBerry devices from our server, and these emails are always delivered to BB inboxes.
Occasionally, we watch an email coming into exchange, it is displayed on blackberry but then disappears from exchange.