Then you cannot rely on mail in ballots because sometimes mail gets lost. Really if you want to make sure that every vote must count, no exceptions, then you have to design a new method of absentee voting.
The moment that a ballot has left the voter's possession, it needs to be tracked and kept securely like we do at my local polling place, or else there's no way to count every vote, no exceptions. So we need something extra for absentee or mail-in ballots.
The crimes he pled guilty to are also on the books in New York. I'm honestly a bit surprised that we haven't heard about his arrest yet.