One of my college compsci professor didn't know anything about manipulating SMTP headers or manually crafting email messages. Couldn't abuse it too much, but could certainly turn in an assignment 8-12 hours late... because the timestamps would be before the cutoff. Any questions were allayed with "oh, you know email. Strange things happens, delays and all that".

We weren't even sending email on a public server, we were just using email on the local compsci server. Checking our messages with pine/alpine. The excuses didn't make any sense... but....