[Maultasche]

I don't know about the rest of the country, but in California the postal service will still deliver mail-in ballots even if they are not stamped. The counties will reimburse the postal service for the costs of the unstamped ballots.

It's not well known, but the counties would rather pay the postage costs of unstamped ballots than have the ballots be returned and the voter possibly not being able to vote.

It would be nice if that were made official rather than an undocumented feature. I'm nice, and I always put stamps on my ballots, but it would be so much more convenient to not have to dig out my rarely-used stamps.