"Generally, tax returns, payments, and other documents sent to the New York State Tax Department are considered to be ontime if they are postmarked by the U.S. Postal Service on or before the due date of the return, payment, or other document. As a result of the 1997 Taxpayer Bill of Rights, taxpayers can also use certain private delivery services, in addition to the U.S. Postal Service, with the assurance that returns, payments, etc., that are mailed on time will be considered to have been filed on time. However, only mail delivered by private delivery services that are designated by the U.S. Secretary of the Treasury or by the New York State Commissioner of Taxation and Finance qualify for the timely postmarked is timely filed/paid rule." To view the entire document, Publication 55 (9/08), click here(PDF).
Note DHL, FedEx and UPS are on the list, but it must be for specific levels of service.