Here’s what to know about mail-in voting for November

President Donald Trump, in his latest efforts to sow doubt about the integrity of mail-in voting as November draws near, suggested this week that voters stress test the election system by voting both by mail and in person -- an act that would constitute voter fraud.

His comments contradicted the law -- it is illegal to vote twice in an election -- but highlighted the real questions voters have about mail-in voting, something many Americans will do for the first time on Nov. 3 due to coronavirus concerns.

The first point of clarity, despite the president's efforts to cast vote-by-mail as riddled with fraud, is that it's a safe and secure option, and election experts have repeatedly dismissed Trump's unsubstantiated claims, telling ABC News that fraud with mail-in voting is exceedingly rare.

"Vote by mail is proven to be successful, secure, convenient and will probably be the safest option for voting this November because of COVID-19," California Secretary of State Alex Padilla, the head election official for the country's most populous state, told ABC News.

Voting by mail could also help poll workers and Americans who choose to vote in person on Election Day avoid exposure to the coronavirus, Padilla said.

"More people who vote early, whether it's in person or by mail, should translate into shorter lines, smaller crowds and a safer experience on Election Day for both voters and election workers," he said.

But the mechanics of voting by-mail differ in each state, since officials are guided by unique election laws and procedures, and it can be intimidating for voters.

Here is some key information about mail-in voting:

The process isn't perfect, but it works

By and large, the election system in the U.S. is a complicated patchwork of rules, different in every state. It isn't always perfect, and election experts acknowledge as much, but it is trustworthy.

The best advice, election experts say, is to get educated on the options -- they go beyond only voting by mail or in person on Election Day -- and act early, so election officials can process all the ballots no matter how they're submitted.

"My recommendation to voters across the country is this: make a plan," Padilla said. "Familiarize yourself with the rules and the deadlines, make a plan and vote early."

But some voters, concerned by inflammatory rhetoric from the president and reports of chaotic primaries held during the pandemic, are looking to their states for assurance that their vote will not just be received, but counted.

Nationwide, a very small fraction of mail-in ballots are rejected during normal election cycles, and typically they're rejected because of simple mistakes that people make when they're voting by mail for the first time. The most common reasons, experts said, are ballots mailed in past the deadline, people forgetting to sign them properly or people's signatures not matching what the state has on file for them.

Still, as more Americans cast their ballots by mail, there is a higher chance that people who never had their votes rejected when they voted in person could wind up not having their vote counted because they filled out a mail-in ballot wrong. To add to the concern, only about 20 states have to notify voters who made errors and let them fix it, while the rest of the states don't.

But experts say there are definitive ways to protect your vote.

"People should demand that they have a fairer system that doesn't actually toss out ballots because of technical defects and gives voters an opportunity to get their ballot counted -- absolutely. People should be outraged that that system allows for that," said Wendy Weiser, director of the Democracy Program at the Brennan Center for Justice at New York University School of Law, a nonpartisan think tank.

"But now that they know that, there is at least some self-help that they can engage in to minimize that chance, and it's already small," she added. "Take that extra time to be very careful, make sure that you know where the signature is, there's lots of instructions, look at your local election officials, they should have instructions on their website."

One way states have increased transparency in the process is by implementing ballot trackers, allowing voters to follow their ballot through the mail in the same way you track a package to your doorstep.

In at least 40 states, new technology will allow voters to track their mail-in ballot's arrival to their house, then track it as it makes its way back through the mail to the election clerk's offices and, finally, check to see if their ballot was accepted or rejected.

For voters who made errors and had their ballots rejected, the next step is to contact the election officials and fix it. For now, that's only allowed in a handful of states -- just 19, according to the latest research from the National Conference of State Legislatures. But experts like Weiser predict that number will grow by November, allowing more voters to have their legitimate votes counted.

The law has already changed in some states this year and decisions are expected soon in more states, including Texas and Minnesota, according to the Brennan Center.

"We will see more and more jurisdictions doing that," Weiser said. "This issue is being litigated in many states across the country and the courts are ruling in favor of voters. It's a reasonable and effective practice, recapturing votes that should be counted but due to some technical error would have otherwise been thrown out under the counting practices."

And for voters whose chief concern is delays by the U.S. Postal Service, states are offering more drop box locations for voters who want to deliver their mail-in ballots directly to election clerks, without waiting on their ballot to go through the mail.

But there are options beyond voting by mail or voting in person, as well. In at least 39 states, according to the NCSL, voters can go to their election clerk's offices and either deliver their mail-in ballot in person, allowing a clerk to double check it on the spot, or cast their vote at a clerk's office in the few weeks ahead of the election.

"I think it's important for voters to know that while the rules may change a little bit from state to state, in most states elections officials are hard at work to provide multiple safe opportunities to vote," said Padilla, California's chief election official.

Why Trump's advice is problematic

As voters fret over their first time voting away from the polls, the rhetoric from the president could potentially add to the confusion -- but there are safeguards in place for voters.

Trump's call for his supporters to vote by mail and then in person to personally verify their vote was counted during a trip to battleground North Carolina on Wednesday was particularly headache-inducing for state and local election officials who quickly scrambled to course correct.

Officials in North Carolina released a memo to warn voters that heeding the president's advice would amount to a Class I felony offense in the state. They also dissuaded residents from following Trump's suggestion to head to the polls -- even just to check the status of their mail-in ballot -- since it could lead "to longer lines and the possibility of spreading COVID-19."

In Michigan, the state's top elections official and chief prosecutor also released a statement to remind voters that "intentionally voting twice is illegal and will be prosecuted."

"Our election system has been stress-tested by three successful elections already this year and in all of them proven that it is absolutely safe and secure," said Michigan Secretary of State Jocelyn Benson. "We have protections in place to ensure election officials track and verify every ballot they send and receive and in every instance we ensure that each person gets only one vote."

In Ohio, too, Maggie Sheehan, a spokeswoman for the state's Republican secretary of state, Frank LaRose, told ABC News in a statement, "Voters are encouraged to choose one way to vote, as any additional effort to cast a ballot will not be counted and unnecessarily burdens election officials."

Although some states allow for voters who unsuccessfully tried to vote by mail to then vote in person to ensure it is counted, which is the case in North Carolina, election experts make clear that it is in fact difficult to "double vote."

The first ballot that is received by election officials from a voter will be the one that is counted, and preclude a voter from voting more than once.

"When an absentee ballot is received and the voter's information on the outside of the absentee ballot envelope is verified, it is standard practice for the voter to be given 'vote credit' on their voter registration file," Wendy Underhill, the director of Elections and Redistricting at the NCSL, told ABC News in an email.

"If that person then shows up at the polls, the poll book will show that they've already voted absentee," she added.

It's also unnecessary for most voters to show up to the polls to check on their ballot since a majority of states start processing ballots before Election Day.

North Carolina and Ohio are among 35 states, plus the District of Columbia, that will begin processing mail-in votes before Nov. 3, according to the NCSL, providing voters time to find out if their ballot was accepted or rejected, without showing up at a polling location.