[jcrawfordor]

Mail-in ballots are linked to a voter permit (outer envelope) which serves the purpose of maintaining the pollbook, that is, ensuring that each voter casts only one vote. This prevents ballot stuffing.

Mail-in ballots are sealed in a tamper evident fashion inside of the permit, to prevent modification. Because opening the envelope would probably damage it, a duplicate enveloped (forged permit) would need to be produced to modify the ballot. In most cases a duplicate ballot would also be needed, which presents its own obstacle, although ballots are not generally intended to be protected against forgery.

The postal service is backed by a particularly strong set of criminal laws which generally make a felony to interfere with the mail. This is of course on top of laws protecting the voting system from tampering.

The outer envelope (permit) is a sworn statement and signing for someone else's ballot would be perjury, a felony, in addition to other laws around voting that likely exist in the state.

None of these measure are perfect, but combined they make vote-by-mail fraud difficult to achieve on a meaningful scale. Remember that, to be effective, voter fraud needs to be successfully committed not once, but many times. The difficulty of each case and general history of harsh prosecution of small-time fraud creates a significant disincentive to try.

[coldcode]

Sadly this only works if you have a Post Office, which we in the US may not have in November.