Spammer using my domain name

I have a domain registered that is not live (no home page) but is set up through a domain registrar simply to forward all emails to a web email account.

The problem is that some spammer is using my domain name to send spam, and my web account is catching all the delivery failure notices.

The spammer does not have control of the domain, but is simply making it appear that emails are coming from my domain, which they are not.

I don’t know how to stop this. The registrar is not any help and won’t reply to my emails. Any ideas on how to proceed with stopping this action? Is there anything I can do?