That is false. Washington and Utah also vote primarily by mail and both allow ballots to be received after the election.

Washington allows ballots to be postmarked the day of the election: https://www.sos.wa.gov/elections/dates-and-deadlines.aspx

Utah allows ballots to be postmarked the day before the election, so long as they are received before noon of the day of the county canvass (generally, the day after the election but as late as ten days after the election, depending on the county). https://www.vote.org/utah/

(I have participated in election litigation in multiple states. I know more about election law than you do. You will not win this battle.)