The Best Nonprofit Email Subject Lines of 2015

What's the best email subject line? Easy: "Free pizza in the lunchroom."

Somehow, that didn't make it into "The People's Choice: Best Subject Lines of 2015," a study by digital-marketing agency Informz—but there is a ton of killer info on the most effective and engaging subject lines nonprofits and associations used last year. The study collected data from more than 80 million emails sent in 2015 as part of an A/B subject line test and 58 million emails that had open rates of more than 40 percent, analyzing keywords, patterns and trends.

The word-cloud above shows the most commonly used words in those subject lines, but the study also includes a detailed look at why certain subject lines performed well, A/B testing strategy, pre-headers and more. Here are some of the highlights:

• Personalization. It's common knowledge that personalization works, but it's always nice to see the numbers. The study found in an A/B split test that "[First Name], Your Membership is About to Expire" had a 13 percent better open rate than the non-personalized "Your Membership is About to Expire" (56 percent against 43 percent). The study also noted that many organizations are experimenting with personalization in other data fields—company name, membership expiration date, geographical data—with early success.

• Numbers. The study found an uptick in subject lines using numbers in some capacity—most often as a way to convey urgency. This approach was notably effective for membership-renewal emails that included a date in the subject line. "Your Annual Renewal Notice 2015-16" had an 86 percent open rate, "Renew your 2015-16 Membership" posted a 67 percent open rate, and "Early bird rate expires Oct. 5" yielded a 52 percent open rate. (Note: The most interesting thing here might not be the high open rates, but by how much "Your Annual Renewal Notice" outperformed "Renew Your 2015-16 Membership." The latter has a clear call-to-action, but still had a 19 percent lower open rate than the former, which had no call-to-action. The study doesn't indicate whether these subject lines were tested against each other, so it's difficult to make a one-to-one comparison, but it's curious that in similar subject lines, the one without a call-to-action won out.)

• Have a little fun! There's a natural tendency to stay conservative in subject lines, and that makes sense. No one wants to come off as unprofessional, or worse, offend donors or potential donors. But the study makes a compelling case for punching up subject lines with a bit more humor and informal tone. "Even organizations that deal with serious subject matter are finding ways to add some creativity and lightheartedness into audience communication," notes Informz. "Results in head-to-head tests show that audiences respond well to humorous ways of communicating ordinary business topics."

Three examples (open rates in parentheses):

• "It's a trashy party, and you're invited!" (35 percent) outperformed "Join us at the Red Clay Valley Clean Up!" (28 percent)
• "Uh-oh, your membership is expiring!" (35 percent) outperformed "[Organization Name] Membership Renewal" (29 percent)
• "OMG, HMF!!" (35 percent) outperformed "Harvest Moon Festival - Sign up now!" (28 percent)

• "Thank you" messages. If you're not thanking donors for their contributions, you're doing it wrong. (We've covered that here, here and well, pretty much everywhere.) And while there's some debate over how frequently you should say "thank you," there's no debating how well simple "thank you" emails perform. According to the study, "'Thank you' for making a real difference" had a 66 percent open rate, "Thank you for all you do!" had a 65 percent open rate, and "A Heartfelt Thank You" had a 63 percent open rate. The lesson: Don't overthink your "thank you" message subject lines. Simple and direct works best here.