I've been having, intermittently, a similar problem.  And no, I don't think
it's spammers picking up my addy off of a NG.

I replied to a friend, using an addy that we just use between us.  And I
ended up with a message listing nearly a dozen bounces for addy's all
starting with 'carl'.  I know they're not in my eddress book, and by looking
at the header I'm pretty sure they're not a part of the message that I got
from him.  So somewhere along the line a spam attack is being initiated
using the original message as a transport host...or something like that...

I've checked and rechecked...as has my buddy.  Nothing seems to be amiss on
either out systems or the eMail.  Is it possible that there's something
amiss on my eMail server?

Any thoughts would be *most* appreciated...

Fred Ranger