Disable mail server

[Spriggsy]

Hi,

I have a website with a domain that was transferred from another server recently. This domain receives a lot of spam email, which happens to be overloading our server and sending the website down.

My question is, how can I disable the mail server altogether in Plesk? The domain doesn't have any email accounts associated with it so there is no need for us to have a mail server at all.

Thanks for your help.