https://www.snopes.com/fact-check/mail-in-ballot-voter-fraud...
What's True
While no U.S. government agency officially compiles state-by-state data on voter fraud, and requirements for mail-in voting vary by state, analysis by elections experts shows that fraud is slightly more common with mail-in voting than in-person voting at polling places.
What's False All types of voter fraud in U.S. elections is minuscule in comparison to the number of ballots cast, according to elections experts. Taking that into consideration, it is problematic to make comparisons between types of ballot-casting systems and erroneous to claim mail-in voting "substantially" increases the risk of fraud.