By Ellie Kaufman, CNN

(CNN) -- States are bracing for controversy as they work to ensure that Postal Service postmarks and other tracking will back efforts to prove mail-in votes are sent on time. They're seeking to avoid lawsuits and other issues about unclear markings that have dogged some primaries and could mar ballot counts come Election Day.

In primaries this summer, some ballots that lacked a postmark but were received on or near Election Day were invalidated because they did not have a stamp from the post office indicating they were received in time. The issues come as the US Postal Service faces questions over its mail delivery and whether it will be able to handle an onslaught of mail-in ballots for the general election.

In New York, so many absentee ballots for the primary were invalidated because they lacked a postmark that voters won relief from a federal judge in a lawsuit to get some of the formerly disqualified ballots counted. And in Virginia, the state's Board of Elections this week adopted a regulation requiring that absentee ballot mail include intelligent mail barcodes, another way to track where a piece of mail is in the system.

In Nevada, the Republican National Committee filed a lawsuit against a law the state legislature passed last week changing certain provisions to make it easier to vote by mail in the November election. One of the provisions is that if an absentee ballot is received by 5 p.m. three days after Election Day but is not postmarked, it will be counted. The lawsuit claims this provision, along with others in the new legislation, is unconstitutional.

Many states add a postmark requirement to mail-in ballots to ensure that the ballots were sent before or on Election Day, trying to prevent votes submitted after Election Day from being counted.

"They don't want to punish you for slow mail, but they want to make sure you weighed in before or on Election Day," Jessica Levinson, a Loyola Law School professor who focuses on election law, told CNN. "You have to have some proof of that so we don't have these endless elections."

But as USPS undergoes leadership changes and cuts overtime pay for overwhelmed postal workers dealing with an onslaught of mail while homebound Americans avoid visiting retailers in person, some election experts are wondering if the post office can handle the expected increased volume of ballots in an unprecedented election cycle.

"Imagine that you get past those barriers, you've registered, you get the ballot, you send it in by the day you think is safe, but then the government-run postal service breaks down and fails you, by no fault of your own. That truly is the dystopian nightmare scenario," Levinson said.

The problem

While requiring a postmark on an absentee ballot is designed to ensure the piece of mail was sent before Election Day and that it doesn't get thrown out because of slow mail delivery, it is not a perfect indicator of when a piece of mail has gone through the postal system -- in part because not all mail receives a postmark.

Business class mail, a type of mail where a business can prepay postage on envelopes in order to avoid costs for the person sending the mail, does not automatically get postmarked. That has already caused problems in at least one primary.

When New York decided to send absentee ballots to all eligible voters in April, the New York Board of Elections chose to send prepaid postage. As a result, when voters mailed back their ballots, many were not postmarked, even though the Postal Service had been notified of the change, according to a federal judge's order that ruled that some ballots must be counted.

While business class mail is not usually postmarked, "USPS has a longstanding policy of postmarking election mail," court documents state. It was the first time New York had mailed absentee ballots to all eligible voters, and the first time they had used prepaid postage on them.

Democracy Fund senior adviser Tammy Patrick said this is why local election officials need to communicate with their local postal workers early in the process. USPS rules and regulations are "vast," Patrick said. They are "not the sort of thing that every employee knows," so it's important to make sure they know that election mail should be postmarked if that is a requirement for the ballot to be counted, she said.

"The challenge is it's quite possible -- until this moment where states are actually adopting this process -- those processing plants probably have never seen those ballots come in before, so they may not even know that that's a rule," Patrick said.

Even though New York election officials communicated with their local post office counterparts about postmarking election mail that was marked as business mail, thousands of ballots still were not postmarked.

"Despite the Postal Service's best efforts, there is uncontroverted evidence that thousands of absentee ballots for the June 23 primary were not postmarked," the judge's decision states. "This could be due to a number of human or mechanical errors."

Federal Judge Analisa Torres argued in her decision that because "evidence showed that" invalidated ballots "were mailed on time," they should be counted.

Thirteen percent of ballots in the hotly contested New York 12th Congressional District race between incumbent Rep. Carolyn B. Maloney and challenger Suraj Patel were not postmarked, the documents state.

"Ordinarily, we don't think of the US as having a national election authority, but in an election where 50 million votes are cast by mail, the USPS becomes that election authority," Stanford Law professor and election law expert Nate Persily told CNN.

New technologies

Postmarks were originally created to ensure that people would not reuse stamps, canceling out the use of a stamp by placing a larger giant stamp -- a postmark -- on top that signifies when the post office has processed a piece of mail.

But technology has developed since the invention of the postmark. USPS has many other ways of tracking mail, including intelligent mail barcodes, or IMBs, and tracking systems individual mail users can sign up for to better follow their own mail.

Some states, like Virginia, are proactively changing regulations from simply needing a postmark on or before Election Day to include other forms of tracking technologies. Virginia's election board passed a regulation to require all counties to use intelligent mail barcodes on their absentee ballots last week.

"The heart of it is just making sure the information from the postal service tells you when they obtained it," Patrick said.

It's possible technologically to track every piece of mail, from when a voter puts a mail-in ballot in a mailbox to when it is received by an election official, US Election Commission Chairman Ben Hovland said. It just isn't used by USPS at the moment, but creating that system and implementing it before Election Day would be costly.

"There have been legislative conversations about having USPS creating end to end tracking" for election mail, Hovland said. "And that's certainly something I would like to see in place."

"We have the capability to do that and relatively speaking it wouldn't be that expensive to have a system like that put in place at USPS," he added.

Vote early

If voters want to ensure their mail-in ballot is counted, election experts urge them to mail their ballots early.

"Do it now. If you haven't registered to vote yet, do it now. Don't think about it. When your ballot comes with enough lead time, make a decision and send it in. That's one thing you can do to not overwhelm the system," Levinson said.

USPS recommends sending a ballot a week before "the due date established by state law," a letter outlining election mail guidance states.

Some states, like Maryland, Connecticut and Michigan, are setting up drop-off ballot boxes for voters to hand-deliver their ballots before or on Election Day if they don't trust USPS to get it to election officials on time. Voters can also walk into any post office and ask for their ballot to be postmarked in person.

If voters are concerned, Patrick recommends voters drop off their ballots in person at the post office.

"That is literally when they would put the postmark on right there at the window, and then it's guaranteed to be postmarked," she said.