The spammer is using your address as the From address. It's not hard to do
since you simply have to tell an SMTP server what the originating address is
and it will just say "OK". Not much you can do about it.

"I" wrote in message
el...
I get periodic reports from my service provider, listing all blocked junk
mail. There are at least 10 spams per week where the sending address is
my own address. How is this possible?