Or How do they do that

[laserblazer]

or, can I stop them doing that? I've just started getting SPAM emails supposedly coming from me.

[powdarrmonkey]

Or How do they do that

 

Because incoming mail servers don't necessarily have a way to tell whether the original mail was from you or not. It was never originally part of SMTP.

 

Can you stop them? It depends how your mail is done, do you have a mailbox with someone or do you do your own hosting?