-----Original Message----- > I think it would be easier to just accept only emails for your domain(s) at > your mta (postfix or exim), then enable the antispam filter on exchange and > configure it drop (not reject / bounce) any messages to invalid addresses.
That's a very bad idea-- legitimate senders will sometimes mistype addresses, and having their messages disappear into a black hole with no notice to the sender is... suboptimal. -- You can always enable a catch all,