Vote-by-mail (VBM) ballots are increasingly central to electoral participation in the United States as well as in other countries. As the prominence of voting by mail grows, so too does the complexity of the rules governing this voting method. We focus on deadlines for returning VBM ballots, a subject of ongoing litigation in the U.S. and a consequential matter given VBM voters’ dependence on mail delivery for timely ballot delivery. In many states, VBM ballots delivered after Election Day are rejected outright, independent of postmark, but Nevada is an exception. Leveraging data from Clark County, Nevada, across five statewide elections that have taken place since this state instituted universal vote-by-mail, we show that VBM voters who are young, new to VBM voting, and registered Republican are disproportionately likely to have returned their VBM ballots after Election Day, all things equal. This implies that state policies on VBM ballot deadlines do not affect all types of voters uniformly. Even though Democratic VBM voters in Nevada are less likely to return late ballots than Republican VBM voters, they are more likely to vote with mail ballots in the first place. This latter point is consistent with the positions of the Republican National Committee and Donald Trump’s campaign for president, which prior to the 2024 general election jointly filed legal challenges against Nevada’s flexible VBM deadlines. Our results highlight the importance of VBM ballot receipt deadlines and the extent to which these deadlines play an increasingly important role in the American election ecosystem.