Someone is spamming from one of my web addresses, how do I stop it?

Thanks Broni for cleaning up my computer.

Made me think perhaps this is a good place to ask about another security problem. I have a web domain we use for email, using the whatever@ at my custom site name. com kind of set up, and someone has been spamming from it. It is registered via go daddy.

We get returned email that someone is using garbabge email@ at my custom site name .com .

What can I do to stop that?

First, change password for all mailboxes on that email server

change admin password to the server itself

if that doesn't stop it, contact Go Daddy support and have them install or configure Spamassassin