We’ve been collecting campaign emails for the last few months for a project we call the Message Machine. If you’ve followed the project you may already know that campaigns have been using increasingly sophisticated strategies to target emails they send out, often sending variations of each message to different people based on their demographics and past behavior. We’ve been asking readers who get emails from the campaign to send them to us. More than 500 readers have sent in more than 10,000 emails since we first launched, with subjects like “Let’s win the damn election” and “Obamacare hurts job creators.”

Today we’re giving everybody access to that trove of messages.

What We’ve Found

So far we have found that the campaigns have been sending on average two variations of each email, but we’ve seen as many as nine variations of a single email. Most often the variations are small, and based on whether (and how much) the recipient has donated in the past. But sometimes the variations are more interesting.

For example, last week the Obama campaign increased attacks on Mitt Romney’s tenure as the CEO of Bain Capital. An email the campaign sent to supporters last Thursday, outlined five issues the campaign said Romney was hiding about Bain and his tax returns.

There were actually at least two variations of this email. The email that was sent to the majority of people in ProPublica’s sample simply stated five simple arguments against Romney — for example, “Mitt Romney refuses to release multiple years of taxes, ignoring decades of precedent.”

But there was also a much longer variation of that email, sent to a smaller group of people in ProPublica’s sample, which lingered longer on the subject, laying out a series of lengthy, probing questions and declaring that the tax returns were important because “presidents make important decisions for this country, and Americans ought to know the motivations behind those decisions.” The alternate message pulls in details including that Romney’s father released his returns during his bid for the Oval Office, and attacks Mitt Romney’s “fundraising ‘bundlers’,” suggesting that those bundlers might get special consideration in a Romney White House.

This isn’t the first time Obama has attacked Romney’s past in an email. An email sent on June 22 highlighted a Washington Post article about Romney’s history with Bain. ProPublica has seen two variations of that email as well. Both variations start with the Post’s article, then diverge significantly.

The first focuses on President Obama’s plan for creating jobs, trumpeting an Obama “jobs plan that could put up to a million people back to work.” But in the second variation, Obama’s plan disappears, and in its place is an attack on Romney, saying his plan sends “jobs outside our borders,” and later notes, “there’s a word for people who say one thing and do the opposite.”

Perhaps unsurprisingly, the campaigns target their core supporters differently than less committed recipients. On July 9, the Romney campaign sent two variations of an email, based on whether or not the recipient had joined a Romney campaign social network called “MyMitt.” Members of MyMitt received an email about “President Obama’s expected billion-dollar reelection campaign,” and were asked to help raise money from their friends and family. Those who weren’t MyMitt members received an email promoting MyMitt, promising recipients they’d be able to “find out about campaign events in your area, sign up to volunteer, make calls from home to get out the vote, fundraise online, and so much more” if they created an account on the network.

Neither campaign responded to requests for comment.

What’s at Stake

According to Eitan Hersh, an assistant professor at Yale who studies the effects of campaign targeting, the data backing these email blasts is extensive. Campaigns have close to 1,000 pieces of information about every voter in the country.

“They know each voter’s name, address, basic demographics, vote history, and whatever other data they can scrape from voter registration files,” and that the better funded campaigns “also have predictions about voters’ consumer habits.” But Hersh notes that targeting is a high-wire act, and guessing wrong can hurt.

“Campaigns mistarget all the time,” Hersh said. “When voters are mistargeted, they might see the campaign as pandering to a group they don’t belong to. They might think the candidate has different values from themselves.”

But the campaigns have been taking that risk. They have been investing heavy in the sophisticated data analysis discipline known as “data science.” Romney’s campaign has recently beefed up its online operations and targeting capabilities, and the Obama campaign has gathered a large team of data scientists who are mining the campaign's voter database.

Message Machine is powered by curious readers who want to understand how modern campaign messages are targeted. If that describes you, and you receive political emails from a campaign, please forward them to emails@messagemachine.propublica.org. Once you send your first email we’ll email you back with a link to set up your account and as we get more emails we’ll be able to show you how campaigns are targeting you.