[fabian2k]

Other countries get preliminary election results the same day even with hand-counted paper ballots. So even that isn't impossible.

[vlovich123]

You can also use statistical techniques to audit results that are for the most part automatically tabulated by machine.

[0x457]

Some stakes couldn't start counting mail-in ballots before the election day. That slowed down counting a lot.

[arrozconcosas]

Mail in ballots are even less secure

[horacemorace]

Source?