Oregon's had voting by mail exclusively, and, it _automatically_ registers voters in a number of places, so unless you are fully off the grid, you're pretty much gonna get a ballot. Consequently, Oregon has had consistently higher turnouts in most elections.

Each vote gets the signature reviewed by a person, one at a time. I actually had my ballot put on hold this year because the signature wasn't quite close enough - likely, since I probably just flippantly scribbled something on the package. They quickly mailed out another registration form where I basically re-signed the ballot for additional information.

Ballots can be dropped off into several boxes, that don't even go through the postal service.

Additionally, most counties have phone and email notifications for you to track your vote. That's how I got my notification, 2 days after mailing it in, that my ballot was under review.