If a tax return (including documents required to be attached to the return and any other documents required to be submitted in connection with the filing of the return) or any other document specified by the Commissioner of the National Tax Agency has been submitted by mail or correspondence delivery, it is deemed to have been submitted on the date shown by the date stamp on the mail or item of correspondence delivery (if there is no such indication, or if the indication is not clear, the date found to correspond to it based on the number of days normally required to deliver the mail or item of correspondence delivery).