Well I read that document you've provided as strong evidence that mail in voting is safe. You've sourced a document that is from the "mail voting is unsafe" team, and they've only been able to find a very few number of such cases, spanning thirty years (it goes back to 1990 at least), and almost all of those cases were caught before the votes affected the outcome.
Can you maybe explain your thinking?
Have you done the math? The document you reference is absent of impact analysis, even vague on the numbers. 1,071 incidents but how many actual votes? How many votes were actually cast? How many were caught before they were counted? Let's take Alabama. 14 reports, but actually first four are all the same incident. So 11 reports. Not off to a good start there. Nine of the remaining were single instance voting. Two were a conspiracy. One conspiracy was caught, in 1994 when it occurred, but is labeled as "Disposition: 2005", which I initially assumed meant that they were caught in 2005, and had gotten away with it. But in fact they were caught at the time because they submitted 1,400 votes in a county of 7000 people. The one that got away with it was caught at the time, and earned the role of a city commissioner of a city of 68,000 people. And yet the person was elected anyway, despite the evidence. So you've got "14" incidents, that are really only 11, and only 1 that got away with in a small city election where even they were caught yet allowed to win. So with just this one state, of the 14 claimed, there was only 1. So for 1071 that's 76. Over 30 years. There are 20,000 cities in the usa. So ~600,000 elections of all sizes they found 76 instances of successful fraud, and only in non-state-wide elections. And that's just me spending thirty minutes with your primary document.
What's interesting is that the Heritage Foundation didn't publish that math. Didn't get into detail.