sadly, my experiment with gmail as my universal outbox was not to be. turns out that gmail transforms the "from:" address of every message sent through its smtp server to "[account]@gmail.com," regardless of what's been specified as the correct "from:" address by my mail client. ineffective for my business email, so that's that. the setup's still valuable for incoming mail; i'm just abandoning it for outgoing.
i can understand why google does it, but it's still bad form.