N.Y. Suffolk County Tax Act § 40-a
The lien of a mortgage, duly recorded at the time of the sale of any lands for non-payment of any tax or assessment thereon, shall not be destroyed, or in any manner affected, except as provided in this and/or the succeding section. The purchaser at any such sale, or those claiming under him, shall give to the record holder of the mortgage a written notice of such sale requiring him to pay the amount required to redeem the lands as provided in the succeeding section, within six months after the time of filing of evidence of the service of such notice with the county treasurer. Such notice may be given either personally or in the manner required by law in respect to notices of non-acceptance or non-payment of notes or bills of exchange. If redemption be not made pursuant to such notice, the mortgage shall be deemed to have been satisfied of record at the time of such sale.
Within one month after the service of any such notice, the purchaser or any person claiming under him shall file with the county treasurer a copy of the notice given, with the affidavit of a person, certified as credible by the officer before whom the affidavit is taken, that the notice was duly given and the manner in which it was given.
If the county treasurer shall be satisfied that the proper notice has been duly given, and if the premises have not been redeemed within the prescribed time, he shall give to the purchaser or those claiming under him, a certificate of non-redemption by the mortgagee, which shall include a statement of the date of sale and a statement that such notice and proof of the giving thereof, has been filed as hereinbefore provided which certificate may be recorded and filed in the office of the recording officer in which the mortgage is recorded, whereupon it shall be the duty of the recording officer to note on the margin of the record of such mortgage that it has been discharged as of the date of sale, together with a reference to the book and page in which such certificate of non-redemption has been recorded.
N.Y. Suffolk County Tax Act § 40-a