Answer:
The term "official check" officially means nothing. It's not a defined term in either the Uniform Commercial Code or Reg CC. If the check is drawn by (signed by) a third-party non-bank bill-payment company, it's neither a cashier's check nor a teller's check. The definitions of each of those "next-day" items requires that the check be drawn by a bank. You appear to have handled the check properly.
First published on BankersOnline.com 9/24/07