Our users are coming in to the office in the morning with unexplained 25+ read receipts relating to old meetings. The time the read receipts arrive in the mailbox appear to be 1am-3am when clearly nobody would be in their mailbox. Any idea what may cause this, sounds to me like some sort of maintenance task. I think some users reported that old meetings also vanish from their calendars, so say a meeting from 8 months ago vanishes in line with the phantom read receipts. Any theories welcome. Exch 2010 by the way.