More likely, someone is simply "spoofing" your email address. It's simple to make an email look like it's coming from anyone at all, so it may look like they have managed to hijack your email address, when in reality they have not. We recommend using spamcop.net to see where the email is really coming from. You can even report them from that website.
Unfortunately, since this really has nothing to do with the server or their operation, there isn't anything we can do if someone chooses to fake your email address for SPAM.Â They are not sending mail using our server. There is nothing to do. They are not accessing the SMTP in any way. If you forward a bounced message back intact (header included) we can troubleshoot it further.
Most likely someone forged your info....anyone can send out an email using the wrong info.......and it's not personal.........spammers have programs that harvest email addresses and then randomly use those domain name addresses to send to and to send as "from." This is a common spam / spoofed address technique.
It is also common for a virus infected computer to do this same behavior....harvesting addresses and then sending out mails using them in the FROM field.
Generally, if you are using a default line to catch all randomly addressed mail, you will be well served to delete it and list only approved addresses in email forwarding. This will reduce spam and the spam bounces. (See this article for details)