N.Y. GCM Law § 82

§ 82. Mailing rules; holidays. 1. Timely mailing.--If any claim,\nstatement, notice, petition, or other document (including to the extent\nauthorized by the director of finance, a return or a declaration of\nestimated tax) required to be filed within a prescribed period or on or\nbefore a prescribed date under authority of any provision of this part\nor of the named parts is, after such period or such date, delivered by\nUnited States mail to the director of finance, bureau, office, officer\nor person with which or with whom such document is required to be filed,\nthe date of the United States postmark stamped on the envelope shall be\ndeemed to be the date of delivery. This subdivision shall apply only if\nthe postmark date falls within the prescribed period or on or before the\nprescribed date for the filing of such document, determined with regard\nto any extension granted for such filing, and only if such document was\ndeposited in the mail, postage prepaid, properly addressed to the\ndirector of finance, bureau, office, officer or person with which or\nwith whom the document is required to be filed. If any document is sent\nby United States registered mail, such registration shall be prima facie\nevidence that such document was delivered to the director of finance,\nbureau, office, officer or person to which or to whom addressed. To the\nextent that the director of finance shall prescribe by regulation,\ncertified mail may be used in lieu of registered mail under this\nsubdivision. This subdivision shall apply in the case of postmarks not\nmade by the United States Post Office only if and to the extent provided\nby regulations of the director of finance.\n 2. Last known address.--For purposes of this part, a taxpayer's last\nknown address shall be the address given in the last return filed by it,\nunless subsequently to the filing of such return the taxpayer shall have\nnotified the director of finance of a change of address.\n 3. Last day a Saturday, Sunday or legal holiday.--When the last day\nprescribed under authority of this part or the named parts (including\nany extension of time) for performing any act falls on a Saturday,\nSunday, or legal holiday in the state, the performance of such act shall\nbe considered timely if it is performed on the next succeeding day which\nis not a Saturday, Sunday or legal holiday.\n