Limit incoming email

Hi all,

So I have configured ScrolloutF1 on a separate machine, and it does a wonderful job. However I'm now faced with the issue that some people seem to be emailing the main server directly instead of going through email records.

How hard would it be to configure IW to only accept email from 1 IP (or subdomain) ?

I hope this makes sense, if not let me know and I'll try again :)

Kat