How did the Obama campaign use direct marketing during the 2012 election?

What will be an ideal response?

Much of the $690 million raised online by the Obama campaign resulted from carefully targeted and tested e-mails. Every day, the campaign used small groups of supporters to test as many as 18 different versions of e-mails varying in subject line, amounts requested, and sender. The winning combination went to the broad base of tens of millions of supporters. Campaign analysts found that a casual tone (such as the word hey) was often effective in subject lines and that supporters seemed to never tire of the e-mails.