The Obama campaign has released new information about the email marketing program used to organize and mobilize supporters, particularly for fundraising. The campaign reports that most of the $690 million raised online is attributable to emails, many of which were put through rigorous subject line testing of up to 18 different versions. The key learnings from the process were that many of the biggest breakthroughs were from the unlikeliest tactics, and also that all breakthroughs had a relatively short shelf-life, requiring continuous testing.