Hence my bit in brackets.
Pretty easy to manipulate in this day and age. It's a shambolic system. As I said earlier, even if there is genuinely is not any election fraud, it looks very fishy. For anyone involved.
I do see your point and like with the Georgia vote counters all being sent home with 10% to count it just looks dodgy as fuck even though that isn't necessarily the case.
Maybe postal voting should have an earlier cut-off (if you've not done it by the day of the election it's kind of on you and why ask for a postal vote in the first place?) or have special collection/delivery to ensure each vote is collected and counted and the voter can track it to make sure their vote has been processed (although I think they already have something akin to this in place). Of course part of the problem was the Trump-supporting Postmaster General appeared to be deliberately making it so that ballots were taking a long time to be sorted.
If you haven't posted it a few days from the election then maybe they should say they will have to take it to a local polling station on the day to be put in a drop-box to ensure it gets there on time and will be counted, but it would have to be ensured they are done carefully because this would likely have some ballots posted that related to a different state (hence why they asked for a postal vote in the first place) so they need to be easily distinguishable. This of course will only open up more accusations of fraud and in theory make it easier.
You could argue that get rid of the electoral college and do it by popular vote and the need to be in a particular state is null and void - only those abroad on polling day really need to worry (along with the infirm, housebound, hospitalised etc). But at the same time this is also potentially even more open to fraud as people can vote somewhere, drive a few hours to a different state and try and vote there so you need a system that can tell who has and hasn't voted that is available in real time nationwide with a few hundred million people on it. With their tech expertise over there it should be possible (but if not we could always send Dido Harding to sort it for them I guess)
There's not an easy answer as each method presents its own problems and snidy fucks in politics will exploit each and every one of them.
*sorry, this turned into a bit of a thinking out loud post.