That sounds like an open invitation to fraud, especially if you are talking about, e.g., paper ballots for optical scanning. What is to stop party organizations (think Democrat) from filling out the ballots for people who they consider elderly and/or disabled and voting a straight party line for them? Doesn't even pass the smell test.
That system sounds even more subject to corruption than the old system of voting on paper ballots at a public polling place.
Better to spend some public money on public voting precincts to safeguard some integrity in the system.
The voter has to sign an application for a mail ballot and mail it back to the administrator of the election. The administrator has to verify that the person is a registered voter, and if that is correct, then sends the ballot packet to the voter at the already registered address on the voter master list - it won't be sent anywhere else.
The voter receives it and votes the ballot and seals the ballot in the ballot envelope, then puts that envelope into a mailing envelope and has to sign that envelope and mail it back to the administrator. A Signature Verification Committee made up of a judge and Democrats and Republicans, compares the two signatures and if they aren't the same, the ballot is thrown out.
That is only one way to check for ballot fraud in mail ballots, but there are other checks that happen also to find fraudulent ballots.