Old Outlook trick I used at the office. We had a department manager who put read receipts on all his emails, including forwards and CCs . A manager who sent about 50 emails a day on a slow day; and was about as technical as a bag of rocks, yet was the director of a technical support team. Manager enters office, unlocks his computer. I assume he is about to forward an email to everyone, that, more than likely, the whole team was all included on already.
Sure enough, forwarded email to the team with a read receipt from the manager shows up in my inbox.
I read it and I am prompted to send a response.
Search for all emails from that manager, select all , there are approximately 1500 emails from the last year.
Mark all as unread, mark all as read, click yes when prompted to send a response.
Repeat rapidly at least 20 times, until strangled cries emerge from the managers office, then panic sounds, then desk pounding, swearing.
IT guy shows up at the managers office, and emerges 10 minutes later.
Looks at me knowingly, smiles evilly, but says nothing. The manager never said anything about to me about it, but the read receipts stopped.