Vote-by-mail is cheaper (no polling places to run), increases voter turnout (which is why it’s universally opposed by the Republican party), and actually reduces fraud risk because it leaves a paper trail and removes the opportunity for voter intimidation at polling places.
It's perfectly fine to believe that this is a reasonable tradeoff for increased turnout and general enfranchisement, but it's not going to reduce voter intimidation.
I think making a claim either way about voter intimidation is silly. The most important points are to increase voter turnout and to reduce large-scale fraud.
How would this be enforced?
Very silly.
Citation needed. And also, is that number more than the number of people who don't vote at all because voting in person is too much of a hassle?