N.Y. Comp. Codes R. & Regs. tit. 9 § 2508.1 : EXECUTIVE DEPARTMENT — Division of Housing and Community Renewal — Rent Stabilization Regulations — Emergency Tenant Protection Regulations — Miscellaneous Procedural Matters — When a notice of paper shall be deemed served

(a) Notices, orders, petitions for administrative review, answers and other papers may be served personally, by mail, or electronically, as provided in an operational bulletin issued pursuant to section 2507.11 of this Title. Except as otherwise provided by section 2510.2 or Part 2511 of this Title, when service other than by the division, is made personally or by mail, a contemporaneous affidavit providing dispositive facts by the person making the service or mailing shall constitute sufficient proof of service. When service is by registered or certified mail, the stamped post office receipt shall constitute sufficient proof of service. Once sufficient proof of service has been submitted to the division, the burden of proving nonreceipt shall be on the party denying receipt.
(b) When a notice of appearance has been filed by an attorney, service on the attorney shall be deemed proper service as if made on the party or parties represented.
(c) Unless otherwise expressly provided in this Subchapter, no additional time is required for service by mail of any notice, order, answer, lease offer or other papers, beyond the time period set forth in this Subchapter and such time period provided is inclusive of the time for mailing.
(d) Unless otherwise expressly provided in this Subchapter, no additional time is required to respond or to take any action when served by mail with any notice, order, answer, lease offer, or other papers, beyond the time period set forth in this Subchapter and the time to respond is commenced upon mailing of said notice, order answer, lease offer or other paper.

N.Y. Comp. Codes R. & Regs. Tit. 9 § 2508.1