Building a great subject line usually falls within the “subject line best practices”. These include important points like:

• Keep it to less than 7 words.

• Get straight to the point.

• Personalize it if you can.

• Ask a question or use a hook.

• And more…

These are loose ideas that most email marketing tools will mention to help you create a subject line. But often, following these best practices is just the first step and, even after checking every box on the list, subject lines still don’t drive engagement.

In order to find the best options for subject lines takes a lot of trial and error. Some audiences react differently than others. In order to get a better understanding regarding how your particular audience responds to the limited options you may have for your subject lines, it’s necessary to test out a bunch of strategies to find the working formula. 

Subject Line Testing

Why is this important? Have you ever seen the scene in a movie where the main characters are trying to get into a club or room and have to come up with a password on the spot? The window on a steel door slides open and a gruff bouncer hollers “what’s the password”. Well quite obviously in any of the instances of this movie trope, the characters have to hurriedly come up with potential passwords until they luck out. While they do that, someone walks up to the door, gives the password, and walks right in which usually frustrates the main characters.

In essence, you are the characters in the movie looking to get into the “super secret club” aka being one of the few emails your customer reads. The customer decides whether or not to open your email solely on the subject line (and your brand awareness). Companies with good brand awareness and great subject line use can stroll into an inbox and convert with general ease. So how do we get the right subject line?

There are a few ways to do this and, more often than not, people starting out with email marketing may use less than ideal options to get their subject line formula down. I would really just recommend using one method:

Subject Line A/B Testing

Subject A/B Tests can help if you are trying to decide between two or more ideas. Generally, an A/B test in any sense of the word is testing two options and comparing each of their successes to one another. There will be an option A and an option B. Using this test on your subject line, you can find the better subject line and automatically send the winning subject to the rest of your audience.

In order to get the most out of your A/B subject line test, I would recommend having at least 500 people in your list. The smaller the list, the less necessary testing two subject lines at the same time is. It may make more sense to test subjects as you go and focus primarily on building your list. Before moving on, make sure your list size is 500+.

Constant Contact Subject Line A/B Testing 

Lucky for us, these subject A/B tests are included within the framework of email scheduling in Constant Contact. 

After building your campaign and getting it ready to send, hit the continue button at the top of your email builder. You will see the “Sending Info” section of the email sending options. 

Turn on the switch:

Add the constraints of the A/B Test. 

1. Subject line option A and subject line option B

2. Sending percentage (at the far right of each subject line) dictating what percentage of your total list do you want to test each subject line out on.

3. Time delay or how long do you want to run the test for before declaring a winner subject line.

Whether you send the campaign immediately or schedule it for a later date, the A/B test will run when the campaign is officially sent to your list.

Using this test will assure you are using the best possible subject line out of the two options you are given. Testing may not stop there. Try different ways of structuring your subject lines in future campaigns as well as different time delays to see how people react. 

To learn more ways to enhance your open rate, check out the Constant Contact Trail Guide.

Mailchimp Subject Line A/B Testing

Unlike Constant Contact, A/B subject line testing is not part of their email sending options. However, there are a few ways to send a A/B subject line test in Mailchimp. It all depends on how technical you’d like to get. Additionally, there is no way to automatically pick a winning subject line and send it to the rest of your list like you can with Constant Contact without detailed automations and a paid plan (you need at least the Essentials Plan).

Segment Sending

This method is a little touch and go but it is free. In order to get the most out of A/B testing using segments, take note of the total number of contacts are within your audience as well as when your contacts have subscribed to your list. The easiest way to divide your list down the middle is to use this info to decide on a “median date” to separate your list. Your goal is to find the date that has half of your list before it and half after it. Here is the process I typically follow:

Setting Up Segments

1. Pick a random date between the creation of your account and today’s date.

2. Go to Audience > Segments

3. At the top right of your screen, select “Create Segment”

4. Where it asks for the criteria for the segment, fill in the information similar to what is is below. Change the date to whatever date you chose in the previous step.

5. Press “Preview Segment”

After you preview your segment, is the number shown half of your total list size? If not, at the top of your new segment press “Edit Segment” and tweak the date until it is.

After you’ve found the median date, save the segment and name it something along the lines of “A/B Segment 1” or anything else that fits.

Next, at the top left click the drop down arrow and select the “Select All” option. Navigate over to the “Tag All” option that appears and create a temporary tag. I would just name it “A/B Test - Group A”.

Sending the Emails

After setting up the Segment and Tag, go to your campaign you’d like to test. Click the arrow to the right of the edit button. A copy of that email will pop up. Rename both emails, one to “[Campaign Name] A” and one “[Campaign Name] B”.

For Campaign A, click the edit button to pull up the email send menu. Fill out the necessary information (Subject Line and Preview Text) and then navigate to the “To” section.

Click “Edit Recipients” and under Segment or Tag, select the Tag you created and save recipients.

Next, go to Campaign B and go to the Recipients > Segment and Tag, and click “Group or New Segment”. Create a segment using the criteria found below (Is not tagged with the tag you created.

Follow your typical send processes and your emails will be sent to two different audiences.

The 50/50 Mailchimp Automation

Within your Mailchimp account, you should have a menu item on the left side that says “Automations”. If you have never used this tool, you should absolutely look into it. Mailchimp has an immensely powerful automation toolkit that can automate a large amount of your email marketing processes. One feature that will help us with our A/B testing is their 50/50 automation flow. Unfortunately, to activate this automation requires you to have at least an Essentials Plan.

Once you have activated your plan, you will have access to activating Customer Journeys (or Automations). Navigate to the Automations tab on the left side of your dashboard. Click “Overview” and then “Create Journey”.

Every Mailchimp Automation has to start somewhere. Click “Starting Point” > “Contact Activity” > “Manual Add”. Now when you add your audience to this automation, they will be funneled through the journey.

Next, drag into the automation the “Percentage Split” journey point. Set the percentages to 50/50 (this is the default value).

On one of the paths, drag a “Send Email” journey point.

Build your email and apply the necessary send details.

Exit back into the customer journey page. Navigate to your finished email and click the three dots at the top right of the journey point. Click them, select copy, and paste it onto the other path.

Change the subject line to the other option and you’re done. It should look something like this:

When your customer journey is active, click “Edit Settings” then select “Manually Add Contacts”.

Add your entire audience by either pasting it in or creating a segment that captures your entire audience. The easiest way to do this is to use the “was after” criteria and your accounts creation date. This will capture your entire audience with ease.

Once your automation is active and your audience is loaded in, your contacts will flow through the workflow and be sent one of the two emails.

Comparing Results

After starting either campaigns, you should give it between 48 - 72 hours. Once this time has elapsed, you can compare the two emails. Compare open rates, click rates, purchases, unsubscribes, and more to get an understanding of which subject line did better.

Within Mailchimp, either of these methods work best if you have a large list and use smaller test segments to test out subject lines before sending the main campaign. Alternatively, it is a great way to test subject line formats for future campaigns to find out what type of subjects work best for your audience.

Subject Line Testing AI Software

If you’d like to look outside of your email marketing software, there are some AI software that will actually write subject lines for you using simple input forms. My favorite tool I usually recommend for clients is called jasper.ai. Jasper.ai has a free tool that can write subject lines for your consideration for future campaigns.

Input the title of your email, select the creativity you want the AI to put into the subject line and frase.io will output some subject lines to consider that have all been checked for plagiarism. These subject lines tend to be a little too long so I would recommend shortening it to fit the constraints of subject line best practices. It’s best to use these as ideas to create your own shorter subject lines. It is your choice whether to use them in conjunction with the A/B testing strategies we discussed or on their own.

Conclusion

Using the A/B Subject Line testing methods we went over may be somewhat time consuming up front however they make a great impact in your future campaign’s success within your audience. Additionally, it has the ability to teach you more about how your audience responds to certain types of subject formats and, with Mailchimp, allows you to dip your toes into the powerful Automation tools. The Subject is the key to an engaged contact list and cracking this code will get you in the super, secret club of email marketing success.

Please reach out if you have more questions on email automation or if you are looking for more customized automation buildouts.