He may be trailing Sen. Bernie Sanders in the delegate count, but former South Bend, Indiana Mayor Pete Buttigieg is leading Democrats in at least one category: email — specifically, Gmail. More campaign emails from Buttigieg’s campaign landed in the primary tab of Gmail’s inbox than other candidates, an analysis by The Markup found. Gmail’s primary tab is considered by many to be their main inbox.

Gmail has a huge chunk of market share among email users, ranging between 25 percent and 27 percent, with its 1.5 billion active email addresses. Reaching these users is crucial for any email campaign.

The Markup used a new, clean Gmail address anonymized with Tor to sign up for email lists of 16 presidential candidates and other groups, and it compared results over four months. Presidential campaign emails landed in the primary inbox only 6 percent of the time, the experiment found. Of the 43 emails the Buttigieg campaign sent during that time, 63 percent ended up in the primary inbox, 9 percent went to the “promotions” tab, and 28 percent went to spam.

Of the other Democratic candidates who are still in the race, all had significantly lower percentages of their campaign emails land in the primary Gmail inbox during The Markup’s survey: former New York City Mayor Michael Bloomberg had a 17 percent rate; the Sanders campaign was at 2 percent; Sen. Amy Klobuchar was at 1 percent; and the campaigns of former Vice President Joe Biden, Sen. Elizabeth Warren, and businessman Tom Steyer had a 0 percent primary inbox rate.

President Trump’s campaign sent zero emails, and former candidate Beto O’Rourke, whose inbox rate was also zero during the campaign, even had the email announcing the end of his candidacy cast into the spam folder.

With political campaigns receiving a significant portion of their small-dollar donations from email solicitations, reaching donors is particularly important for Democrats in this election cycle. The Democratic National Committee required candidates to have 65,000 unique donors to qualify for the first two official DNC debates and 130,000 unique donors to qualify for the third and fourth debates. (The DNC scrapped the donors requirement before last week’s debate in Nevada.) Federal Election Commission figures showed candidates spent more than $6 million just through the first quarter of 2019 to rent or acquire email addresses and other contact information, according to watchdog site OpenSecrets.

The report points to a situation that may not be obvious to most Gmail (and other email client) users: your inbox is every bit as curated as your Twitter or Facebook feeds, and it’s based in part on your browsing history. When Gmail started sorting emails into distinct inbox tabs in 2013, marketers complained that the open rates on their email campaigns suffered, but users seemed to like the attempt to declutter their emails and to reserve the primary inbox for “the mail you really, really want.”