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Subject Line Testers: To Use or Not to Use

According to a 2019 research done by Radicati, a US based technology market research firm, approximately 250 billion emails are sent out every day. So...

According to a 2019 research done by Radicati, a US based technology market research firm, approximately 250 billion emails are sent out every day.

So, to make sure the email you sent is opened, it is very important that your subject line stands out.

Many email marketing service providers carry out subject line testing, which may or may not give you the targeted conversion goal. This is because, the success rate of subject line testers depends on your organizational values and customer preferences.

Read on as we comprehend the scenarios where and how subject line testers work.

Why Is Subject Line Testing Important?

Testing enhances the subject line attempting to increase open rates of email campaigns. Subject line testers give suggestions based on what has worked out for clients before, taking references from old case studies.

The subject lines derived by these testers are based on trends and it can be customized as per the organizational needs.

As these subject lines are derived through artificial intelligence, it saves unimaginable amount of time for email marketers.

It draws attention to trivial aspects of the subject line such as the kind of special characters to be used and the number of characters that can take you to the spam folder. Unnecessary words are removed, and subject line is reduced to bare minimum, which gives a concise straightforward subject.

Overall, it quality checks the subject line without a customer interaction. 

Subject Line Tester – Does It Work?

Yes. Subject line testers do work, BUT it is not as simple as it looks. Generalized subject line testers give suggestions based on the current trends and modules that have worked in the past. Sometimes, these trends may work in favor of the marketing strategy.

Let’s see how.


It makes a huge difference if you’re approaching your subscribed audience base, who have opted-in to hear from you or if you want create awareness among new customers about your brand.

A past customer or a lead who has requested for information about your brand or is looking forward to hearing from you, will most likely open your mail.

In this scenario, a concise – strong – informative subject line would work beautifully. The reason behind this is, your customer is aware of your product and only requires a brand recall.

On the other hand, a new customer will need a short- attractive – interactive subject line. This will not only grab the attention of the reader but also encourage interaction and eventually conversion.

Factors like audience proximity, geographic location, gender, economic status, and age will also matter. A personalized subject line based on segmentation of audience will ensure that the email is opened.


Timing is very important in this fast-paced dynamic marketing industry. Creating a subject line based on the customer relationship shows the subscriber that you care.

It is important to know your customer’s time zone or demography to create the perfect subject line.

For example, if it’s a promotional mail for Christmas sale, you can try and use emojis of gifts or stickers in subject line to bring in the festive touch to the mail.

Not only that, it is important to know the time gap between the last contact made with your subscriber.

For example, if you are a mechanic, it would be a good idea to send reminders to customers who had their last oil change 3 months ago. This call to action would give them a push to what they already need.


There are various tools offered by email marketing campaign providers based on what kind of goal you want to achieve.

For example, this subject line tester offered by Zurb, lets you preview your subject line and mail output on different mobile phones. 68% of emails are opened by mobile phone users , so keeping in mind a mobile friendly email subject line will give you those bonus points.

Tools provided by provide a detailed evaluation of your subject line based on effective delivery, sense of urgency, appeal and share suggestions to make necessary changes to meet marketing standards.

Furthermore, there are tools to check if your email copy might trigger spam filters or what you can do avoid landing up in the spam folder.

What Can Go Wrong In Testing?

To begin with, when you enroll for a service, there is no assured guarantee that the given evaluation by subject line testers will help you achieve your goal. This is because Internet is a dynamic industry with constantly changing trends.

As subject line testers derive results only based on old case studies and trends which have worked for clients in the past, it might not be applicable to a specific target audience.

Subject line testers based on artificial intelligence lose individuality and a personalized touch. In 2020, most people know that marketing mails are not individually sent, and such subject lines will make the emails evidently impersonal and distant.

Moreover, there is no data or information about the audience’s likes and dislikes, and as a result, the performance of the email will be unreliable in automated subject lines.

For instance, an email by Campaign Monitor had the subject line “What’s really happening between the US and Turkey?” This mail fared well with 28.1% open rates, which is good enough to indicate that the subject line is of good quality.

When the subject line was checked on a tester, it didn’t fare well and suggested changes to be made.

The test results indicate the subject line needs a lot of improvements. If the content writer had made the changes according to the instructions given, they might have wasted time for another copy which might have ended up getting even lower open rate.

Perfecting A Subject Line

  • Keep your subject line concise and sensible.
  • Use special characters and upper case.
  • Make your subject line attractive using emojis without going too much over the top. 
  • Get as personal as you can to drive subscriber interaction.
  • Know your audience, their preferences and dislikes.
  • Use words like “New” “Today” “Urgent” or “Alert” to create a sense of urgency and prompt the next action.
  • Avoid using spammy words like “free” and “$$$”.
  • Multiple punctuation marks may trigger spam filters and there are chances of your mail getting blocked.
  • Spelling error in the subject line is big no-no.
  • The from name email address also makes a difference, for example- would be read and would most likely be treated as spam.

Wrap Up

The subject line is as important as the content of the email. A perfect subject line reaches out to an individual reader rather than the mailing list. Unless the subject line is curated according to the demography of the target audience, it would most likely end up in the trash bin or even worse, the spam folder!

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Kevin George

Kevin is the Head of Marketing at Email Uplers, one of the fastest-growing full-service email marketing companies. He is an email enthusiast at heart and loves to pen down email marketing content. You can reach him at or connect with him on LinkedIn.



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