Back in college I worked for my school's IT department doing on site support for staff. I was exposed to a lot of very interesting WTFs at that job but one I remember was a ticket filed by an admissions counselor regarding emails from her supervisor and others not being delivered. She'd missed an important discussion because after a certain point she was not recieving the messages. I checked the conversation on another machine to verify she was still being CC'd, which she was. It was pretty puzzling until I had her supervisor re-forward part of the conversation to her, while I watched her inbox I saw a message arrive and immediately vanish. She had no other folders and it wasn't in deleted items, spam, or anywhere. It turned out that she'd setup a few email filtering rules to keep her from having to read profane emails, there was a whole list of words that if matched to an email would cause that email to be deleted outright, not just placed in deleted items.
Her boss's email? Well, at one point he invited everyone out for cocktails.