Disable E-mail for entire domain

[webcatal]

Is there a way to completely disable a domains e-mail ability. I have about 50 domains on my server and in a couple cases the client does not use e-mail at all on our server but the spammers somehow get mail to be delivered or sent from the default address. Can that be disabled anywhere. I want to only do this on a couple domains but not all. However it was possible to disable the default e-mail account from sending or receiving any e-mail for all accounts and still have php be able to send mail, that would be even better.

[Lyttek]

If you don't create any email accounts, and set the default address to :fail: I think that'll do it.

[webcatal]

I don't have any accounts created other than the required e-mail (or default) which is the username of the account. I can set the default address to :fail: but the default e-mail is still able to send and receive. I want to completely disabled e-mail from being able to be sent or received to a chosen domain. This would include disabling the ability for scripts such as PHP to be able to send mail as it usually uses the default address for the domain (when phpsuexec is installed).