Earlier quoted context omitted.
Mail in voting is still secret ballot - you have an internal "secrecy sleeve" that is in turn mailed in an outer envelope. The outer envelope signature is compared to the signature on file, and then the internal envelope is removed but is not opened in the same location. https://www.sos.wa.gov/_assets/elections/wa_vbm.pdf https://www.cnn.com/2020/09/11/politics/barr-secret-vote-fac...
That doesn't stop a determined group of canvassers from going door to door and pressuring people to fill out their ballots on the spot while they wait on their doorstep. It's also a perfect time to offer a bribe or incentive for a speedy completion. There's no way that any form of remote ballot is going to be as secure as doing it in person. It's just not possible because you will never know the provenance. Like most…
At least it is not a problem I know about where I live.