When I was an undergraduate student at CMU, the email systems supported fuzzy common name matching, so even though my Andrew username was jrc, you could email e.g. john@andrew.cmu.edu and it would try to deliver that (if unambigious). If you added a plus sign (+), the system would do an exact match instead of a fuzzy match, so in practice my email address was jrc+@andrew.cmu.edu. (Note: that is no longer my email address.)