Exactly what the other replier said -- with current protocols almost certainly not possible, and even with complete access to *@mydomain.com it would likely be

Exactly what the other replier said -- with current protocols almost certainly not possible, and even with complete access to *@mydomain.com it would likely be a serious hack, brittle in many ways, and not robust in others. But with a new protocol underlying, I could see this all being handled automatically. (maybe -- I haven't walked through this with a technical person).