Originally Posted by coodem
If someone is spoofing your email address from another terminal, you have no real control over this, apart from reporting it to your ISP or changing your email address
I wonder whether the problem might be as simple as this: A contact of Tosh McCaber's has contracted a mass mailing virus. That virus is sending out spam and/or itself with a forged "from" line giving Tosh McCaber's address, even though the e-mail is actually coming from the victim's machine. When the spam is undeliverable as addressed, it gets bounced, but bounced back to Tosh McCaber as that is the "from" and/or "reply to" address.
Maybe I've missed something in the description which shows why this suggestion is a load of rubbish, but I make it FWIW.