A user created a new Appointment in his Outlook 2010 calendar and sent an invitation to several other users. After getting a confirmation from the attendees, he received multiple Read Receipts from them as well.
The Read Receipts state, that the invitation message was deleted while it was unread.
The user had no configuration for Delivery or Read Receipts in Outlook.
Where do those receipts come from?
Exchange Server Version: Exchange Server 2010 SP1 RU1
Client Version: Outlook 2010