Mail Rules

I've got a 100% working ISPConfig setup and I love it - it's handling multiple domains wonderfully. Thanks guys - have a question though.

I want 1 domain to deliver mail locally. By that I mean no outgoing mail from this domain at all and only allow certain domains to email in. Can I use mail_access or the mail_transport table to get this working? (I don't see any OFFICIAL documentation on these two tables). I don't want to start changing settings that breaks my current implementation.

Any developers that can provide some insight?

Zack