I'm sure you can find a couple more old SMTP threads on which you can plug your product

LoaPost is an interesting solution (though you've got a pretty significant/embasassing typo in the WinXP quickstart docs - I'll tell you where for a small editing fee ) to tunnel SMTP traffic from the localhost to your server and then on to the Internet, using what I assume is non port 25 traffic to bypass all the systems that would block that. There are a number of questions that it brings up - almost as many as it answers. Most notably is whether it is creating an open relay or if there are limits on where it accepts emails from. If you're turning individual computers into open relays there's a big problem there.

S.