[ZeroID (Brent)]

As Paul states you have been spoofed. most likely not even your fault. Your email address has been 'harvested' from some website, email trail or someone elses PC and been used to spam others in the hope it might be seen as a trusted sender.
Pretty common and little you can do about it unfortunately. To minimise further situations I always send any dist list mail using BCC ( Blind Copy Circulation ).
Hope fully it will slow down in a while as the list becomes corrupted and blocked by others and the spammers will move on to another collection.
We see them all the time in the mail filters