Has Barack Obama ever invited you to dinner?

If you were one of the tens of millions of people on the president's campaign email list this cycle, your inbox was full of odd dinner invitations, personal questions and leading statements such as "So," "It doesn't have to be this way" and "Meet me for dinner."

Now that the campaign is over, staffers have finally explained those odd fundraising subject lines and their apparent success to Bloomberg Businessweek's Joshua Green.

"We did extensive A-B testing not just on the subject lines and the amount of money we would ask people for," Amelia Showalter, director of digital analytics, told Green, "but on the messages themselves and even the formatting." The team would predict how much money could be generated by each subject line sample.

Profanity was a hit, the phrase "I will be outspent" was a winner and recipients apparently preferred "ugly, yellow highlighting" over something more aesthetically pleasing.

In the end, most of the $690 million the president raised online was through email.

The most successful subject line? "Hey."