I have 4 active sites and for each one of them someone (or several someones) have hijacked the main e mail address and they are sending sp*m with them. I am not receiving any complaints but I do receive all of the bounced e mail and all of the Auto-Replies and notices of the Undeliverables. Not only is it bad for my business and my brand, I consider it theft and would like to know :
A) Who to report it to
B) How to stop it

Thanks for any and all help with this.