Whenever the Commissioner or this Subchapter requires that a bank serve a notice on a customer or creditor, such bank may serve such notice either by delivering it to such customer or creditor or by depositing it in the United States mail, addressed to the customer or creditor at his last address according to the records of the bank, with registered, certified, or first-class postage charges prepaid. However, if the document last mailed to the customer or creditor at such address was returned by the United States Postal Service marked to indicate that the United States Postal Service was unable to deliver such document to the customer or creditor at such address, the notice shall be deemed to have been given without the bank's delivering or mailing it if it is available for the customer or creditor upon written request at an appropriate office of the bank for a reasonable period of time.