Thanks, I'll look into that; it'll simplify it a bit. Anything that is parsed from text output is obviously not super solid but for this application it'll suffice. The MX for the business domains in question is an external service that takes care of spam filtering, address consolidation, etc. The external service also offers better availability than the LAN server that is not monitored 24/7 and that is connected to the internet via single T1. But as a remote service it is not as fast as accessing emails on the LAN, and at peak-times the Internet congestion slows it further. This is a small office environment, and the plan is to "cache" the couple of dozen mailboxes to the LAN mail server. The above configuration will be used to prevent any mail from outside of the external service from finding its way to the local mail server.
In the event the local server fails (since there is no server redundancy), users continue to have full access (albeit slower) to their mailboxes using the external service which is the primary receiver anyway. Ville
