Mail-in voting, also known as postal voting, allows people to cast their votes for an election via post rather than at the ballot box. However the voting method has come under fire from US president Donald Trump, who has previously said there is “tremendous fraud involved” with postal voting.
Mail-in voting procedures in US elections differ depending on the state.
In some American states, all registered voters are able to vote by mail automatically.
Other states have made mail-in voting widely available for people to request, while other states have restrictions in place.
For example, in some states you cannot postally vote without a reason, such as due to illness or serving in the military.
Despite Mr Trump’s claims mail-in ballots can increase voter fraud, this has been widely discredited.
States operate various anti-fraud measures when distributing and processing mail-in ballots around election time.
Checks are carried out to make sure registered voters receive ballots, and that ballots are sent to the registered addresses of voters.
Many voters are required to include their signatures on the external envelopes of mail-in ballots, which can then be matched with a signature matching process.