It's not simply voting by mail, it's voting by mail by not even using official the post office in Romania.
I know that you're probably refering to US, but I don't make any comment about it, because I don't live there, so I don't know what really happened in US.
In Romania some people found partially burned ballots with only opposition votes next to a garbage bin before the elections ended. The proofs of voter fraud couldn't have been clearer. It's supposed to be a scandal, but nothing will happen about it.
https://hungarytoday.hu/discarded-burnt-postal-ballots-scand...