Mail-in ballots are a good idea, especially in COVID times, but the current implementation in the US seems so obviously wrong.
Specifically, allowing ballots to be mailed on the final day guarantees that they can't be counted until several days later. The potential problems generated by that are obvious, even if one doesn't look at the current reality.
Setting the deadline a week earlier would have allowed a reasonable amount of time for the ballots to be delivered and processed, even if not actually counted until election day.
But that's not what they did, and it must have been a deliberate decision.
So what were the reasons for allowing ballots to be mailed up until the end of election day?