Can you explain to me what the problem is with voting by mail? It is something that is widely done in democratic countries without accusations of widespread fraud.
At least here in India (which happens to be the largest democracy in the planet), we don't have the option either for mail-in voting or early voting. There is a national holiday on the day of voting and in case you can't get to the polling booth to cast your vote, then your chance is gone. And why we don't allow mail-in ballots? Exactly because in the past there were numerous instances of fraud performed through mail-in ballots. In low crime countries such as Japan and Korea it maybe a good idea to allow postal voting. But it has failed in most of the other countries.