Read Receipt
Reminds me of an email faux pas back in the late 90's in the days of Lotus Notes.
I was a lowly student in a large multinational chemical company. I had no transport to work so decided to send out an email asking for a lift to work. I'd pay some money to petrol obviously.
I set my out of office up for a 2 week holiday, thinking I'd read the generous offers when I got back.
What I'd forgotten to do was click off the "Request Read Receipt" option in Notes. (Scratch "forgotten", I think to ignorant to realise might be better}
I returned to work 2 weeks later with a straight to the bosses office moment. Apparently my innocent email had setoff a nasty death spiral of read receipt \ out of office mails that crashed the email server. I never asked if it was the whole company.....
When my boss realised I hadn't done this intentionally we had a polite chat about email etiquette and moved on. I never mentioned it to the IT admin nor did he mention it to me!