N.Y. Elec. Law § 11-212
All special federal ballots received by the board of elections before the close of the polls on election day shall be retained by the board of elections and cast and canvassed pursuant to section 9-209 of this chapter. All ballots contained in envelopes showing a cancellation mark of the United States postal service or a foreign country's postal service, or showing a dated endorsement of receipt by another agency of the United States government, with a date which is ascertained to be not later than the day of the election, shall be cast and counted if received by the board of elections not later than seven days following the day of a primary election or thirteen days following the day of a general or special election except that the special federal ballot of a voter who requested such ballot by letter, rather than application, shall not be counted unless a valid application form, signed by such voter, is received by the board of elections with such ballot. All ballots received by the board of elections and all federal write-in ballots received from special federal voters not later than seven days following the day of a primary election or thirteen days following the day of a general or special election, shall be retained at the board and shall be cast and canvassed in the same manner as other ballots retained by such board.
N.Y. Elec. Law § 11-212