However, those who may have received two ballots in this election cycle should be assured there is no reason for concern about the integrity of the 2020 election, experts say.
In fact, in counties where some voters have been mailed dual ballots, officials say the mechanisms to stop multiple ballots from being counted are proof that the voting system works.
"I want to reassure everyone and make you understand that no one is going to be able to send in two ballots from one voter. It won't work," said Bucks County, Pennsylvania, chief clerk Gale Humphries in a press conference on Thursday after the state identified a flaw in its system that allowed duplicate ballots to go out to nearly 1,000 voters.
"It is a hard stop. We've seen two come in, and you cannot record two for one individual," Humphries said, adding that she's tested the system herself.
That's the constant message that election officials have for voters who have received two ballots in the mail, a malfunction that can occur because of printing errors, system errors or because a voter moves and forgets to update their address. Depending on the state, election officials recommend voters destroy the second ballot, mark it so it can't be used or return it to the sender with a message that the voter no longer lives there.
But election officials also have another important warning: It's illegal to vote twice. Voters who do can face thousands of dollars in fines and felony charges -- though more often than not, voters who receive two ballots send both in because of confusion, not in an attempt at fraud.
"We have safeguards in place so that if a voter tries to pull a fast one, we will figure it out," said Nick Jacobs, public information officer for the Washington, D.C., Board of Elections.
"And we are telling all voters that we will pursue all incidences of voter fraud to the fullest extent possible, and it carries with it a $10,000 fine and up to five years in jail," Jacobs said.
D.C. residents have not reported being sent double ballots as a common issue, though Jacobs said it can happen from time to time because the city is one of the most transient in the country, constantly seeing residents forget to report their change of address as they come and go.
But in D.C., as in other states, officials say any double votes are caught because of the unique ID for each mailed ballot and the process of signature verification, where the clerk matches a signature on the ballot against a signature on file for that voter.
And that process forms a pretty significant paper trail.
"There's a record of all of this," from the mailed ballot to the signature to the voter registration data, said Myrna Pérez, director of the Brennan Center's Voting Rights and Elections Program.
The high risk of getting caught is the main reason why voter fraud is less likely than being struck by lightning, according to a May 2020 report from the Brennan Center.
"People don't do it because they're going to get caught and it's the wrong thing to do," Pérez said.
That doesn't mean it's not alarming to voters when they receive two ballots.
"I think it is true that we have underfunded and under-resourced our elections, even in the best of circumstances, and when times are tough ... there's a giant rush and an increase in demand, the cracks in the system are going to be apparent," Pérez said.
But those cracks can be fixed by built-in safeguards, she said, and in the case of double ballots or fraud, "the voter is risking a whole lot because they have a paper trail for what they did.”
Such was the case in Fairfax County, Virginia, when a last-minute decision by the Virginia General Assembly required intelligent barcodes -- allowing voters to track their ballots like an Amazon package -- be applied to all ballots. The decision brought on an unexpected workload for clerks.
"We had to apply [by hand] 150,000 labels to ballots," said Fairfax County elections director Gary Scott. In the process, ballots were sent out twice to about 400 voters.
"It's pretty well up there" in terms of mistakes to avoid as an election official, Scott acknowledged, because "the goal is one person, one vote."
"Everyone is entitled to a vote and we want to make sure we get that right, but we also want to make sure that people aren't trying to game the system."
But Fairfax election officials were able to identify those voters who received two ballots and have since stopped any voters who mailed both back in, most of whom did so by accident. They've also changed their process for reprinting labels to avert any other issues.
"Our system works," Scott said.