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If you’re like most email writers, the subject line can be one of the most daunting and last minute parts of email creation. But it’s one of the key factors in determining whether or not an email is opened, and can affect the amount of attention or revenue you generate. Worse, it can make or break your relationship with your advocates or constituents.

That might seem a little dramatic, but its impact is extensive. When you throw in the fact that there is no one right answer, to the “perfect” subject line, it gets even more overwhelming. On the bright side, there are ways to figure out what the ideal subject line for your audience looks like, and it involves data and testing.

Informz’s annual email marketing benchmark report, read by thousands of nonprofit and association email marketers, helps answer the question of how is my organization’s email program doing, compared to others’? With more and more organizations asking specifically about subject lines, we decided to delve into the specifics of subject line data, to see what we could learn about successful ones.

We looked at data from 138 million emails sent by association and nonprofit marketers in 2015 (that’s a LOT of emails) to see what’s working (and what’s not) when it comes to email subject lines. We tapped into keywords, patterns, and trends of winning subject line test results, and high-performing subject lines, and the results were fascinating. Here are some of the highlights of the Best Email Subject Lines of 2015.

Get Personal

It’s no surprise that personalized subject lines are among the most tested and successful subject lines. Any time you can find a way to personalize your messaging, results tend to be better. In the case of subject lines, personalization drives response. In head-to-head tests, subject lines with personalization consistently outperform non-personalized subject lines. “First Name, Your Membership is About to Expire” beat out “Your Membership is About to Expire” by garnering 30% more opens.

While inclusion of the recipients’ first name is the most popular way to personalize, organizations are also experimenting with incremental data fields and seeing strong results. For example, company name, membership expiration date, and geographical data such as city or state were up-and-coming performers. The subject line, “Your membership has an expiration date of ‘Expiration Date,’” generated an open rate of 52%, which is far above the benchmark average of 35%.

Make Them Laugh

This next trend is one of my favorites, because as someone who receives a lot of email, I know that this type of subject line appeals most to me, and it looks like I’m not the only one. This year’s data analysis showed an increase in the number of marketers testing out clever and funny subject lines, and that they’re winning over a more traditional or routine type of subject line.

Subject lines that stand out in the inbox, and stir positive emotions in the recipient, are boosting overall audience engagement. Concerned about testing a fun and informal subject line with your serious-minded recipients? There’s good news. Even organizations that deal with serious subject matter are finding ways to add some creativity and lightheartedness into audience communication. Results in head-to-head tests show audiences respond well to humorous ways of communicating ordinary business topics. Here were some of my favorites in this category:

It’s a trashy party, and you’re invited! (35% open rate) versus Join us at the Red Clay Valley Clean Up! (28% open rate)

OMG, HMF!! (35% open rate) versus Harvest Moon Festival – Sign up now! (28% open rate)

Everyone Likes Free Stuff … Right?

The words complimentary and free are synonymous with each other and either one could be used to describe something that comes at no cost. This type of offer is popular in email marketing, and it’s no surprise that audiences tend to respond more often to offers of no charge items in A/B split tests. But what word works better – free or complimentary?

Complimentary is a word that conveys receiving special treatment, and may be the more appropriate word to use, based on what you are giving the recipient. Complimentary services outperform “free” services, such as complimentary guest registration, complementary airport transportation, and complimentary concert tickets.

Still, the word “free” performs quite well, too. It’s our observation that the word “free” works in many — but not all — situations. For example, “Register Today – Free Breakfast on Saturday” (58% open rate) performed well above the 2015 benchmark. People respond well to invitations for free food, too. The following subject line sums our observation up nicely: “Did someone say free food?” (68% open rate). When appropriate, consider testing these popular words to see if they help boost open rates.

Feeling Inspired?

Hopefully these trends and tests have your marketing wheels spinning. If you’re ready to see how trends like these and others mentioned in this subject line guide can impact your open rates, start here:

  • Test! Subject line testing is a win-win proposition. It takes the pressure off of you – the marketer – to come up with the world’s greatest subject line, and puts the power and decision-making into the hands of your audience. The message is for them. Let them help you uncover the types of subject lines that work for them. Is personalization the way to go? Or maybe sprinkling in some humor? These strategies might work well for some organizations, but not for yours. The only way to know is to test.
  • Don’t forget your preheader. Preheaders play a supporting role with the subject line. It’s an extension of the limited space you have in a subject line, helping you further describe and support the email’s contents. This area is vastly underutilized, but when taken advantage of, will supplement the subject line and provide more information to recipients.

Whatever you do, remember that the message is for your audience – not you. Be clear, concise, and have fun figuring out what works best for recipients that will help you achieve the open rates you want to see. For additional information on the best email subject lines, be sure to check out the Best Subject Lines of 2015.