This morning, there was a planned power outage in my building. As best I can tell, the building's internet gateway failed to come back up afterwards. The person who can fix the problem won't be in until Monday. (We shall omit the grumbling about this setup.)
Thus, if you email me, you'll get various bounce messages that say things like "Email couldn't be delivered after three hours; will try again later". This doesn't actually mean I didn't get the email; it also goes to a third computer system that's still on, and which I can use (albeit awkwardly) to read my mail.