Subject Line Best Practices

There are many different factors that make subject lines engaging. Some readers respond to personalization while others look for a word of thanks. Some look for humor while still others look for a way to feel like a part of something special. In fact, each of these strategies works well, and the key to understanding how to draw your users to your mailings is through testing.

Let’s take a look at some best practices based on Informz’s extensive eMarketing experience.

A/B Testing

Before diving into some example subject lines, you should always take advantage of Informz’s A/B testing option. This process allows you to send two different subject lines to a smaller portion of your target group/audience and then send the winner (the subject line that receives the most opens, etc.) to the remainder. This way, you are using data to ensure that you are sending an engaging subject line. Remember, it may not be a guarantee for success, but it’s certainly better than jumping in blindly!

Top Trends

Based on Informz's research here are some common themes among subject lines that performed well in A/B testing.


Personalized mailings consistently outperform others. For example, using a subscriber’s First Name is far more likely to garner an open then a simple message. The two examples demonstrate this:

Sample Subject Line Open Rate
[First Name], Your Membership is About to Expire 56%
Your Membership is About to Expire 43%


Unexpected expressions of gratitude are an excellent way to draw in your audience. This is especially true when you don’t ask for anything in return! Remember, asking for more can feel off-putting! However, a genuine “Thank You” might be all it takes. The following examples show how some simple kindness can go a long way.

Sample Subject Line Open Rate
Thank You for Making a Real Difference 66%
Thank you for all you do! 65%
A Heartfelt Thank You 63%


Though it falls outside the realm of traditional communication, organizations are free to show their humorous and playful side while still maintaining a professional demeanor. Audiences tend to respond better to a creative way of communicating ordinary business topics – these messages appeals to your subscribers’ curiosity and stir positive emotions. Let’s look at a few side-by-side examples:

Example 1:

Sample Subject Line Open Rate
It’s a trashy party, and you’re invited! 35%
Join us at the Red Clay Valley Clean Up! 28%

Example 2:

Sample Subject Line Open Rate
Uh-oh, your membership is expiring! 35%
[Organization Name] Membership Renewal 29%

Example 3:

Sample Subject Line Open Rate
OMG, HMF! 35%
Harvest Moon Festival – Sign Up Now! 28%


Numbers (dates, monetary savings, percentages, etc.) provide an excellent way to attract subscribers. Dates, in particular, provide recipients with a sense of urgency and a solid goal to work toward. Take a look at the following examples:

Sample Subject Line Open Rate
Your Annual Renewal Notice 2015-2016 85%
$25 in Your Pocket! 38%

Complimentary or Free

While both “complimentary” and “free” are synonyms, each works better in a different scenario. Readers tend to have a stronger association with “complimentary” services (such as guest registration or transportation) whereas the use of “free” is more closely associated with items (a free gift, free shipping, etc.).

Sample Subject Line Open Rate
World Conference: Complimentary Airport Transportation 67%
Free Shipping and Free Gift: TODAY ONLY! 46%

Back to Testing!

Does personalization positively impact your open rates? Or, perhaps your lighter side brings about more opens and clicks. As above, don't forget to use Informz's A/B testing capabilities to let your audience decide the best subject lines! Subject line testing really is a win-win proposition. As a marketer, it actually takes some of the pressure off of you and places it on the audience. Remember, the message is for their eyes!