N.Y. Comp. Codes R. & Regs. tit. 21 § 6.3
The notice of hearing and all other notices, orders and communications from the commission shall be duly served if enclosed in a properly postpaid wrapper, addressed to the person to be notified or communicated with at the address last given by him in writing to the commission, and deposited, as ordinary mail, in a post office, post office box or mail chute maintained by the United States government, or if such notice, order or communication addressed to such person is delivered to such address by telegram or by registered or certified mail or by an employee or agent of the commission. A certificate by an employee or agent of the commission that such notice, order or communication has in the regular course of the business of the commission been duly dispatched or delivered, in a manner authorized by this section, shall be presumptive evidence of proper service. For the purpose of calculating the time of notice, service shall be considered effected upon the date of delivery to such address; provided that, where service is by ordinary mail, service shall be considered effected the third day after the mailing.
N.Y. Comp. Codes R. & Regs. Tit. 21 § 6.3