Notwithstanding the provisions of any State tax law to the contrary, whenever payment of all or any portion of a State tax is required by law to be received by the Pennsylvania Department of Revenue or other agency of the Commonwealth on or before a day certain, the taxpayer shall be deemed to have complied with such law if the letter transmitting payment of such tax which has been received by the department is postmarked by the United States Postal Service on or prior to the final day on which the payment is to be received.
72 P.S. § 8101.1