Progress report: A little more legwork and I'm now there as far as sending deferred messages.
I had to a) designate my ISP as a smarthost, which I've never had to do before, and b) make sure the ISP's domain wasn't listed (inadvertantly) in smail/config as another host on _my_ system. That leaves the pesky 'questionable operand' message, and the rdate problem, for now. --- Bob Bernstein at Esmond, R.I.