Email Subject Line Testing: an Effective Guide

Subject lines are essential elements in email marketing. But how…

Subject lines are essential elements in email marketing. But how do you know your subject line is effective?

Read on to learn about subject line testing and how you can use it to ensure your subject line is intriguing to your audience.

Why Email Subject Lines Are Important

The subject line of your email determines the success of your email marketing campaign. A good subject line commands your audience’s attention and gets them to take an interest in what you have to say.

For example, a large company might not get the attention it deserves if the subject line of its email isn’t intriguing to the recipients.

One of the best ways to get engagement is to create an intriguing subject line that hooks your audience. It caters to their curiosity and makes them read till the end. A good subject line is necessary for email marketing. It is excellent at getting clicks, opens, and conversions.

Several people decide to open an email based on the subject line. It’s the first thing people see, and it has to intrigue and persuade them to look at the following content.

What Is Subject Line Testing?

Subject line testing is a marketing tactic that determines whether a customer or lead opens an email. It is a way to test the power of your subject line and determine whether your message will lead to better response rates.

Subject line testing is the process of determining the best email subject line for your message and your marketing objective. The title of your email is one of the first things people see. It can impact your ability to make a sale, build a connection, or get someone to sign up for your mailing list.

The testing can be done in several ways – automated and manual. With testing, you can optimize subject lines using keywords or phrases that will persuade subscribers to open and read your emails.

How to Test Your Subject Line

To intrigue your target audience with your email subject lines, you need to test them to see how effective they are. With subject line testing, you can determine which marketing email sequences to use and which ones to discard.

The A/B testing is an effective method that uses a direct comparison of email subject lines. Create two variations of your email, changing only one element in the subject line.

Send the email with subject line ‘A’ to a segment of your audience, and that with subject line ‘B’ to the other segment. Analyze the result of both emails, based on response and conversion rates.

Steps for Testing Your Subject Line

Email subject lines are the first impression people have of your email. This makes the subject line an essential element of email marketing. A poorly chosen subject line is a missed opportunity for your email to be read. Getting it right can help you boost your inbox open rates and increase engagement.

How do you know if your subject line is compelling enough? This is where subject line testing comes to play. The following steps will guide you on how to test your email subject line.

1. Determine Your Audience

The goal of testing your subject line is to understand what best appeals to your audience. Before you begin testing, understand your audience and why they might be interested in your email. Format your subject line in a way that makes sense to your target audience and resonates with their thoughts and feelings.

If you are marketing to a specific demographic, ensure that your subject line accurately reflects that demographic. Think about which parts of the marketing campaign, or email content appeals to your target audience and use this information to brainstorm subject lines.

2. Decide What Aspect to Test

As a rule, you should test one element of the subject line at a time. When you try more than one element, knowing which component caused the difference will be challenging.

Determine what aspect of your subject line should be tested. The results would tell you how to optimize your email marketing campaign. Some of the common elements you can try are:

A. Words

Adding or removing a single word can make a lot of difference in how your targeted audience perceives your email. For effective results, A/B test two subject lines that are similar. Consider the following:

  • Marketing 101: How to Make Your Business Successful.
  • How To Make Your Business Successful.

Even with only a slight difference, the results generated from both subject lines, based on clicks and conversion rates will not be the same.

B. Length

An email with a shorter subject line is believed to be more effective than one with a longer subject. However, it is best to determine what works for your target audience. A/B testing a shorter email subject line against a longer one will help you discover what works for your audience.

C. Personalization

Personalized subject lines include the recipient’s name, title, or company. With the help of Customer Relationship Management systems, this approach is now a popular email marketing tactic. However, do not assume this will automatically work for your audience. It is best to A/B test this element to see what works best. You can include ‘You’ in one of the two variations of your subject line. Consider the following:

  • Top 10 Marketing Strategies You Need for Business Success.
  • Top 10 Marketing Strategies for Business Success.

D. Design

A slight change in design can be why your email gets more opens and clicks. Design is an essential part of making your email stand out and commanding attention. A/B test all caps versus sentence case, emojis, and even punctuations.

3. Test a Segment of Your Audience.

A/B test only a subset of your primary audience. Divide this subset into two groups, and send each variation of your subject line to each group. Use the results you get to conclude what subject line is most effective.

You can use the winning subject line to send the email to the entire audience. While some marketers use the whole audience to A/B test their subject line, it is advisable to use only a subset. This is so that you don’t risk sending the weaker-performing subject line to half of your audience. To get an effective result, send the email to both audiences on the same day and time.

4. Analyze Your Result.

Analyze both results with the metrics in mind. While open rates and click-through rates are essential, the most important metric to you is conversion rates.

One subject line might lead to greater open rates but lesser conversion rates. As a marketer, your goal is to drive more conversions with your email; this is what you should focus on when analyzing your result.

5. Keep Testing.

Your first test shouldn’t be your final test. If your first A/B test revealed that your audience prefers shorter subject lines to longer ones, use shorter subject lines in your subsequent testing. This time, test for a different element (i.e., personalization or words). With constant testing, you’ll improve communication and get more improved results (i.e., clicks and conversion rates).

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Photo by Solen Feyissa on Unsplash


The email subject line can be used as a soft or hard landing point for the email. Its purpose is to give the audience an idea of what the email is about and gauge their interest.

Subject line testing is an essential email marketing tactic. Through testing, you understand what subject lines are more appealing to your audience. You can then use the winning subject lines to improve conversion rates and make the email marketing campaign more effective.

Frequently asked questions

What is a good subject line for a checking in email?

Let’s take a look” Instead of “Checking in” or “Touching base,” opt for “Let’s look” as the follow-up email subject line. If you told someone to contact you at a later date, this subject line is reminding them that you’ve spoken with them before. It also maintains a friendly tone.

How do you send a check through email?

  • It was interesting to see how everything was going.
  • This led me to think of you.
  • As soon as possible, let’s catch up.
  • I was interested in seeing how I could help.
  • I’d love to get to know what you’re working on.
  • Time as much as you can.
  • I have been missing you and wanted to say hi.

What is the most important part of an email?

The subject line. Subject lines are probably the most important element of an email, as they decide whether a message is read or deleted.

How can you ensure your subject lines are effective?

Keep your subject lines short and sweet so they are effective. Subject lines with short and medium lengths have higher open rates than long ones, which ultimately affects conversion rates (the percentage of people who take action based on your email).

What is an email subject line tester?

Analyzing your subject lines with an email subject line analysis tool allows you to assess their click potential. Also, it helps you optimize your subject line’s length and emotional appeal to increase clicks.

Is touching base a good subject line?

The subject line is also an excellent alternative to overused subject lines such as “Checking in” or “Touching base,” which are both unneeded. Not only do they appear wasteful and disrespectful, but they simply do not work. A 50% failure rate was found in “Touching base”.

What is a good subject line?

Keep your subject lines short, by keeping them at not more than 40 characters or five or seven words. Readers will scan through your inbox very quickly. Only a few words or phrases can stand out and gain the most engagement with subject lines.

What is the purpose of subject in email?

It may be the most important few words in your email that are included within the subject line. You have a tagline, it is your first impression, it’s the reason the recipient will open it, or will not open it. The subject line should tell the reader three simple words: “Tell me more.”.

What is a catchy subject line?

You should write short, straightforward, concise, and straight to the point about your subject line. Additionally, providing sense of humor, scarcity, or fear of missing out (FOMO) will encourage recipients to open their emails even more.

Why is a subject line important in an email?

The recipient must grab attention in the subject line quickly. Subject lines of 50 characters or less are expected to result in 12% higher open rates and 75% higher click-through rates than emails with longer subject lines.

How do I check if my email address is correct?

  • Send an email to the address in step 1. Emails are most commonly valid checked by sending a message to them.
  • Method 2: Password Recovery
  • Google’s Address Search 4
  • Method 5: Email Checker

How do you get the attention of an email subject?

  • Let’s keep it relatively short and clear. Your subject line should be engaging and catch your audience’s attention.
  • Ensure urgency
  • Personalize
  • Ask questions
  • Be honest
  • Use numbers
  • Offer real value
  • Include a call to action.
Email Subject Line Testing: an Effective Guide

Abir is a data analyst and researcher. Among her interests are artificial intelligence, machine learning, and natural language processing. As a humanitarian and educator, she actively supports women in tech and promotes diversity.

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