The trick is to do it without violating the principle of a secret ballot. At least it gets the ballot to the counting center without allowing the Slave Party to pad the total with every illegal in the State.
If the Post Office could check the submission against registration rolls, that would take care of another part of the problem. It’s getting the envelopes to the counting center in a rigorous fashion that matters. Assuring that the ballots are counted properly without knowing the voter ID is a different problem.
The voter voids the right to secret ballot by voting any other way than in-person after ID check.
Chain of custody trumps in that respect.
IMHO
Use special paper. Watermark the paper. Add bar codes to serial number them.