Well, they’re not really.
It’s as if I were at my sister’s house and I wrote a letter (a what?!) and put my return address label on the envelope even though I was sending it from my sister’s house. So if it got returned, it would come to my house, not her house. The spammers are putting your return address on their mail. Unfortunately, if you have a domain, this will happen. I have domains where I don’t even have websites and I get this stuff. Spammers need to get day jobs, they have too much time on their hands.
The sad long and short of it is: there’s not much we can do against it. It’ll go away or die down.
There is one step we can take so you don’t have to get all of the error messages from the junk that gets bounced (because they’ll bounce back to the same address it came from e.g. [email protected]). If you know that you are the “default” address for your domain, i.e. you get [email protected], we should switch it so you only get the emails you want to get, e.g. [email protected] and not [email protected]. Let me know if this is the case and also which domains you do want to have forwarded to you (e.g. newsletter@, contact@, help@, etc.).