Both voting in person and voting by mail have a long history of trustworthiness in the US.
Voter Fraud is Extremely Rare Across Voting Methods
Each voter’s identity and eligibility to vote are verified before their ballot is counted. Oregon, the first state to adopt a vote by mail system, has averaged fewer than one case of fraud per year for two decades (source: Heritage Foundation). Claims of voter fraud are investigated by authorities and can result in criminal charges.
History and Expansion of Voting by Mail
Americans have been voting by mail since the Civil War, when President Abraham Lincoln wanted to give soldiers a way to vote from the battlefield. US troops overseas routinely vote by mail, and several states now hold their elections almost entirely by mail.
Mail Ballots are Resistant to Fraud
Mail ballots require extra steps for validation after they’re returned by the voter, such as signature matching and ballot tracking. Once validated, the ballot is separated from its envelope and sorted for counting. Mail ballots that meet eligibility and validity requirements are counted in every election.
Verification at the Polling Location
Poll books at in-person voting sites say which voters have already received mail ballots. If there are any issues or irregularities, voters are usually offered a provisional ballot that requires additional verification. If a voter submits more than one mail ballot or tries to vote in person after already voting by mail, only one ballot will be counted.
Source: Bipartisan Policy Center