N.Y. GCM Law § 139

§ 139. Mailing rules; holidays. (a) 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 title\nis, after such period or such date, delivered by the United States mail\nto the director of finance, bureau, office, officer or person with which\nor with whom such document is required to be filed, the date of the\nUnited States postmark stamped on the envelope shall be deemed to be the\ndate of delivery. This subdivision shall apply only if the postmark\ndate falls within the prescribed period or on or before the prescribed\ndate for the filing of such document, determine with regard to any\nextension 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\nsection. This subdivision shall apply in the case of postmarks not made\nby the United States Post Office only if and to the extent provided by\nregulations of the director of finance.\n (b) Last known address.--For purposes of this title, a taxpayer's last\nknown address shall be the address given in the last return filed by\nhim, unless subsequently to the filing of such return the taxpayer shall\nhave notified the director of finance of a change of address.\n (c) Last day a Saturday, Sunday or legal holiday.--When the last day\nprescribed under authority of this title (including any extension of\ntime) for performing any act falls on Saturday, Sunday, or a legal\nholiday in the state of New York, the performance of such act shall be\nconsidered timely if it is performed on the next succeeding day which is\nnot a Saturday, Sunday or a legal holiday.\n