The standard advice from marketers on email subject lines is to keep them short, but make them informative. MailChimp says “Your subject line should (drum roll please): Describe the subject of your email. Yep, that’s it.” Constant Contact says “Your subject line should convey not just what’s inside your email, but that the contents are important, timely, and relevant.”
But that may not be good advice for advocacy. The Obama campaign made subject lines teasers rather than headlines: “Something extraordinary”, “A beginning”, “You have to see this”, “Results”, “In his own words”. Of course, there was little chance you’d forget what to expect from their emails, given how many they sent. And Politico has talked about the e-mail subject heading war, with PR staffers writing self-consciously clever lines to get reporters to open their emails.
So what should you use? Simple: whatever gets your organization the best results. Test an informative subject, a teaser, a challenge, something personalized, a question, something forwarded…. Pretty much any email system will let you do A/B testing with a fraction of your list and then send the better-performing email to everyone else. Take advantage – you don’t know what will work best for your audiences until you have actual data from their actions.