The payment never arrived! It has now been more than two weeks. It never cleared at the other end, either. And now my credit card has hit me with substantial delinquency fees. Adding insult to injury, I forfeited over 3,000 points (=airline miles) because you don't earn points if your account isn't current.
I've had to stop payment on the original payment and will submit a new (electronic) payment on Monday after the various systems cycle. Then I will call Diners Club and see if they'll believe my (truthful) explanation and either reverse the charges or reinstate the miles or maybe even both.
But now I hope the original mailed payment never turns up, because then I'd get another service charge for a rejected-payment fee.