HI Tina,
The only thing I can think of in that case is if you at one stage used an email client which would have downloaded them off our mail server. Aside from that I'm stumped!
Jojo 
Nope, never used a client. Always accessed via webmail, since as long as I can remember. I don't even have any mail clients installed on this machine, with the exception of Lotus Notes, used for work - which I keep entirely separate. Don't want my personal correspondence ending up in there.
It's definitely got wiped somehow.