The 5th Circuit Court of Appeals has ruled that all ballots in Louisiana, Mississippi, and Texas must be received by election day. The ruling supersedes any state law concerning the schedule for counting votes.
Furthermore, the ruling sets an important federal precedent for the other 47 states.
From the ruling:
"Congress statutorily designated a singular "day for the election" of members of Congress and the appointment of presidential electors. Text, precedent, and historical practice confirm this "day for the election" is the day by which ballots must be both cast by voters and received by state officials. Because Mississipppi's statute allows ballot receipt up to five days after the federal election day, it is preemted by federal law. We reverse the district court's contrary judgment and remand for further proceedings."
The ruling could be appealed up to the Supreme Court, but that is unlikely to happen before the election. So, it appears that one of the ways to cheat in the election has been eliminated, but several still remain.