N.Y.C. Admin. Code tit. 27, ch. 2 § 27-2095

a. Except as otherwise expressly provided in this code, any notice of violation or other notice, or any order authorized or required to be served by the department under the provisions of this code, shall be served in the following manner on any person or corporation to whom or which such notice or order is directed:


(1) By delivering a copy of such notice or order to such person directly, or if it is directed to a corporation, by delivering a copy thereof to any officer or managing agent of such corporation personally; or


(2) By delivering a copy of such notice or order to any person of suitable age and discretion at the residence or place of business of the person to whom it is directed, or if it is directed to a corporation, at any office of such corporation; or


(3) (i) If service is to be made on an owner of a dwelling, by mailing a copy of such notice or order to the latest business or residence address of such owner as set forth in any registration statement filed by such owner with the department under the applicable provisions of article two of this subchapter;


(ii) If service is to be made on a managing agent of any such dwelling designated under the applicable provisions of article two of this subchapter, by mailing a copy thereof to the latest business or residence address of such managing agent set forth in any such registration statement or designation filed by the owner of such dwelling;


(iii) If service is to be made on an owner of a dwelling who has not filed such a registration statement in relation to such dwelling, or on a managing agent of any such dwelling who has not been designated under the applicable provisions of article two of this subchapter, by posting a copy of such notice or order in a conspicuous place in such dwelling, or by delivering a copy thereof to any person of suitable age and discretion in charge of or apparently in charge of such dwelling, or by mailing a copy thereof to such owner or managing agent at the last known business or residence address of such owner or managing agent.


b. Any such notice directed to an owner of a dwelling or tenant of any space therein need not designate such owner or tenant by name, but shall refer to such dwelling or space by a description which shall be sufficient to identify same and shall state that it is directed to the owner of such dwelling or tenant of such space, as the case may be.


c. Where a designation of a managing agent under the applicable provisions of article two of this subchapter is currently in effect as to any multiple dwelling, any notice mentioned in subdivision a of this section which is directed to the owner of such multiple dwelling shall also be directed to such managing agent, and shall be served by the department on both such owner and managing agent.


d. If a mortgagee or lienor has registered with the department pursuant to the provisions of section 27-2109 of article two of this subchapter, any notice of violation or other notice, or any order authorized or required to be served by the department under the provisions of this code on the owner of a dwelling may also be mailed to such mortgagee or lienor no later than five days after the date upon which such notice or order is served upon the owner, but the department's failure to mail such notice or order to such mortgagee or lienor shall not in any way affect the validity of service of such notice or order upon the owner.