Not funny!

Since about one week we are experiencing a wave of new spam – it´s „undeliverable-spam“ – send under the name of our domain. It´s always a message back from some unkown recipient, that our mail was undeliverable. The mails are sent by some temporarily dial-up smtp servers. So, anyone got a hint what to do? I´m a little bit afraid this spam – wave will kick us on some blabklists.

UPDATE: made a report to the local police – don´t expect much to happen, but want to be sure to have done every imaginable step.