Contrary to petitioner tenant's contention, the promulgation of Rent Stabilization Code (9 NYCRR) § 2531.4, which, in pertinent part, requires a tenant contesting a luxury decontrol petition to retain proof that an answer to the petition was served, lay within DHCR's broad mandate from the Legislature ( see Rent Stabilization Assn. of N.Y. City, Inc. v. Higgins, 83 NY2d 156, 168; and see Matter of Muller v. New York State Div. of Hous. Community Renewal, 263 AD2d 296, 305, lv denied 95 NY2d 763). The record discloses that DHCR complied with Rent Stabilization Code § 2531.4, giving petitioner tenant appropriate notice of his obligation to retain proof of service on the front page of his answer form. While petitioner maintains that a hearing was required to ascertain whether he did in fact mail his answer, and whether it was received and discarded by DHCR because it was not sent by the prescribed form of mail, he did not submit objective proof of mailing of any kind, such as a certificate of mailing, or a contemporaneous affidavit of service giving the date, time, place, content and circumstances of mailing. Further, the tax returns now relied upon by petitioner are not included in the administrative record and should not be considered by this Court. Under these circumstances, DHCR's determination was not arbitrary, capricious or contrary to law.