Ahead of the US midterm elections on 3 November, President Trump continues to make unsubstantiated claims that mail-in voting leads to widespread fraud.
US states have different voting rules and regulations – but every state allows some postal voting, a method the president says he has used in the past.
BBC Verify visited an election centre in Maryland to get a behind-the-scenes look at how mail-in ballots are processed and counted.
Produced by Mabel Pickering. Graphics by Sally Nicholls.