We just transitioned to Exchange 2010 Office 365 Hybrid. About once a day the Exchange server needs to be rebooted, as emails show up in users sent items but do not deliver. They are also unable to receive email. Once the server is rebooted, everything comes through. I did not see anything in Errors in the Event Viewer that seemed to correspond with the timing of this issue. I reviewed the firewall logs and found nothing useful. Any ideas as to what could be causing this daily annoyance?