Millions of Americans are receiving absentee ballot applications from outside groups. Here’s what you need to know.

With fewer than 60 days until the end of the November general election, millions of Americans are receiving a cascade of election mail, and though most of it is legitimate, much of it is not official.

Third parties and outside groups, such as major political parties and voter engagement groups, are ramping up their efforts this year to get out the vote in a number of ways, including sending millions of Americans absentee ballot applications in the mail.

This is perfectly legal, as long as the groups are complying with state guidelines, but it comes with the added cost of confusion to voters and frustration to local election officials who may receive more than one absentee ballot application from a single voter.

With election officials already working around the clock to cope with the mass changes to election law this year -- mainly the expansion of absentee voting eligibility so Americans can vote from home safely during the pandemic -- it can be frustrating to have to process multiple applications from a single voter, who may have been confused about whether or not their other applications were processed.

"Part of the challenge here is that not only more people are sending out applications to voters, in order to make sure voters have an opportunity to vote by mail, but when voters do fill out multiple ones, because maybe they fill it out one day and then a week later because ... they haven't gotten the ballot," Tammy Patrick, the senior adviser of elections at Democracy Fund, told ABC News.

"So voters might be more inclined to fill out multiples. And all of that just continues to snowball in local election offices," she said.

Minnesota Secretary of State Steve Simon said that snowballing can become frustrating for election officials, who have to process multiple applications from one voter.

"It can be frustrating to election administrators who are getting second, third and fourth absentee ballot applications from people who are sending it in with goodwill," Simon said.

On top of that, there is no requirement that outside groups coordinate with officials in the state where they are mailing out election information.

"One of the issues on outside groups sending absentee ballot applications is there's no requirement whatsoever that they talk to us, notify us or say anything. They can just order the voter file, which is a public document we sell for something like 46 bucks to campaigns all the time, nominal cost, and they can just mail them out," Simon added.

The confusion isn't eased by President Donald Trump's frequent attacks on safety of absentee voting, which has undermined the confidence of voters despite it being a safe process.

Just this week, the president told voters in North Carolina to still go to their polling place to vote even if they voted by mail, which is illegal, and set off a string of responses from national politicians and organizations urging voters not to do so.

In what has been dubbed by both Trump and Democratic nominee Joe Biden as the "most important election of our lifetime," groups are working overtime to ensure voters are engaged, including the nonpartisan, nonprofit voter engagement group Center for Voter Information.

The group, which was established in 2004, previously focused primarily on election mail to register Americans to vote, or to help them update their voter registration so they were still eligible once they got to their polling place.

Voting is an entirely different process in 2020 and the Center for Voter Information is adapting to reflect that.

"With COVID-19 impacting elections, we have a responsibility to do all we can to safely increase voter turnout amid this uncertain time. We feel it is vital to keep voters safe and to bring democracy to eligible voters' doorsteps. Since we are non-partisan, we do not send mailers based on party affiliation. We care if you vote, but not how you vote," Tom Lopach, the president and CEO of the Center for Voter Information, said in a statement to ABC News.

The Center for Voter Information is focusing primarily on demographic groups that are typically underrepresented when it comes to voting, including people of color, young adults and unmarried single women in primarily battleground states across the country. Their applications, in states where it is legal, even feature much of the voter's information already filled in for them, in an attempt to ease the burden of requesting a ballot.

Already this cycle, CVI has mailed 34.3 million vote-by-mail applications to registered voters around the country. And with another push in September, an additional 37 million applications will get sent again.

But the system isn't perfect.

In Virginia, for example, CVI sent out a number of mailers to voters with improper return addresses. Their applications, which include prepaid postage, are meant to be returned to county election offices. The wave of mailings sent to Virginians had the wrong addresses and those applications couldn't be processed until they were mailed to the right offices, CVI clarified. A printer error resulted in the confusion, which has since been ironed out.

Their tracking system allows them to see the return rate of voters who are using their applications specifically to request an absentee ballot by mail. And though it is slow to update, so far, over 3 million Americans have used CVI applications across the country.

"We sometimes send several 'waves' of vote-by-mail ballot applications to voters, since people are busy and often need a reminder. We frequently check state databases and do our best to remove the names of any people who already have signed up to vote by mail," Lopach said.

Those waves are in addition to similar mailings that are often sent by political parties working to get out the vote.

"Just as we do every cycle, the RNC is sending out absentee ballot applications in battleground states and our field teams will be aggressively chasing those ballots. Additionally, we are rolling out one of the largest and most aggressive 'get out the vote' programs focused on early voting and Election Day," Mandi Merritt, a spokesperson for the Republican National Committee, told ABC News in an email.

The Democratic National Committee did not immediately respond to inquiries about their mailing operations this cycle.

Receiving multiple ballot applications can take a toll on election workers, Simon said. Minnesota law requires the final application sent in to be the one processed and used to mail voters their ballots.

"From the standpoint of election administrators, and the counties and cities, they tear their hair out because they have to process every one. The rule in Minnesota is an assumption if someone sends a second or third or fourth one in that you always process the one that came in last," Simon said.

Gerry Cohen, a member of the Wake County, North Carolina, Elections Board, said a good portion of applications in his county come from third-party vendors reaching out to voters.

"I've had several county election directors tell me that a huge amount of their requests start coming off these blank forms sent out by the third-party groups. So despite there being a lot of people making calls saying, 'What is this, can I use it?' and being generally panicked, in fact, they're heavily used by voters," he said.

North Carolina, the first state to send out official absentee ballots in the mail on Sept. 4, allowed voters to request an absentee ballot without an excuse this year. Compounded with other changes, the state has seen a 21-fold increase from the same time in 2016, according to election expert Michael McDonald.

"I don't think anyone in past years has ever done this," Cohen said of the huge influx of third-party involvement in absentee ballot applications. "There's been very little of this, even though we've had people to apply for absentee votes without an excuse since 2002. But I don't recall ever having gotten an application [from other groups]."

The applications sent by CVI are identical to the ones sent by the state, Lopach said. Otherwise, according to Cohen, the applications cannot be processed.

CVI works with states before a mailing to ensure that they are legal and effectively differentiated from mailings that the state sends.

"In 2020, we are working in tandem with county and state election officials around the country to make sure that eligible voters have a chance to safely participate in democracy. There's never been a more important time to register to vote, and to know the options for voting before and on Election Day," Lopach said.

ABC News' Kendall Karson and Cheyenne Haslett contributed to this report.