in brazil's case, mail in voting is not allowed at all, all voting must be done physically at public buildings or private schools which are mandated to contribute their space to the voting proceedures, all citizens to vote must come to the building and room they were assigned to months in advance, you wait in line in front of your room, one can cast a explicit blank vote or an invalid one which is called null vote, both are independly and accounted and you can see in the results, ever since this election showing a ID card with a photo is required to vote, with drivers license and the national ID (locally called RG, registro geral, or in englisb would be general register) are valid for this purpose