The Complete Guide to Subject Line Testing


Subject line testing is a crucial part of any email marketer’s role. It is singularly one of the simplest and most effective ways to improve the performance of an email marketing campaign.

But saying it is simple is one thing. So today I wanted to actually take the time to lay out the do’s and don’ts of subject line testing so that every brand, organization and marketing team can succeed in their quest to find better subject lines.

What is Subject Line Testing

Essentially, subject line testing is the process by which you seek to improve the open rate on your emails by delivering the same email to different audiences – one of which sees one subject line, and the second group sees the other. In this way, subject line testing is a very specific example of an A/B Test.

The reason that brands of all types run subject line tests is that it is one of the best ways to improve the overall performance of an email marketing campaign. Because the subject line is one of the first considerations for an email recipient – one of the first things they see along with the sender once an email lands in their inbox – it is one of the most important elements of any email.

Often, a subject line alone will mean the difference between a recipient choosing to open the email or not. So by testing multiple subject lines, we aim to improve the open rates over time.

How to Set Up a Subject Line Test

There are a number of different ways to set up a subject line test:

  1. You can test the entire list. If you are testing an entire list, you simply send 50% of them subject line A and the other 50% subject line B. These results will help you plan for future emails.

  2. You can test just part of a list. You might choose to only test part of the list, so that you can use the results of the test to send the winning subject line to the rest of the names on the list. For example, you might take 20% of your list and split it into two groups (10% each) for the test. Then wait 24 hours to determine the winner before sending the remaining 80%.

  3. You can test programmatic emails. If you have an automated email campaign, one that triggers based on user actions and often includes more than one email in a sequence, you can build tests into your program. Send half of your users down one path and half down another, and run subject line tests at each step in the process. However, here you must remember that the sequence matters, meaning the results of one test at the beginning could impact results of emails that come later.

How to Judge the Results of a Subject Line Test

Judging the results of a subject line test should be quite easy. Remember from the information above that the goal of any subject line test is to improve the open rate of that email. And so it is the open rate that we must measure.

Compare the open rate of subject line A against the open rate of subject line B, and you should get your answer. The email with the higher open rate is the winner.

A few additional things to consider:

  • Allow enough time between the email send and the results analysis. Not everyone will open the email right away. A good rule of thumb is to wait at least 24 hours to declare a winner.

  • Statistical significance matters in any A/B test. A result is considered statistically significant if the confidence level is at least 90-95%, meaning you can confidently conclude that the subject line was responsible for the difference in open rates (rather than chance). This is a great free tool to measure statistical significance.

  • It can be tempting to look at metrics other than the open rate, such as the click through rate. But the subject line will have less impact there. If the open rate on one version is significantly higher, but the click through rate on that version is significantly lower, you might consider what other factors are leading to those results.

What Types of Subject Lines Should You Test

As a general rule, you should test all of your subject lines. There is no surefire way to know which subject lines will perform best for an individual email. And testing is the only way to determine that with any certainty.

But just like anything else that you do, some measure of priority must be determined. Which emails are the most important? How would an improvement in the open rate of each email impact the business at large?

Once you have determined which emails to test, there are some best practices you can aim to incorporate into your new subject lines:

  • Personalization – include the person’s name or other details in the subject line

  • Urgency – convey a sense of urgency around offers

  • Questions

  • Punctuation

  • Less is More – limit the length of your subject line

  • Capitalization – try different ways of incorporating capitalization

  • Active Words

  • Positive language vs. negative language

You can check out this tool from, which calculates a score based on a very specific formula for subject line effectiveness. But remember that that is just a guide and just because a subject line does not score well doesn’t mean that it won’t perform well with your lists.

Best Practices for Abandoned Cart Emails

Ask any business with an online shopping presence what their biggest frustration is, and they’ll probably answer, “abandoned shopping carts.” In fact, there are far too many carts that get items added only to be left behind—and it can be difficult to determine why.

The reasons for consumers abandoning a cart are many. They might be frustrated by the whole process and not want to set up an account. They might feel that there are fees that were tacked on the end that they weren’t expecting. Or they might just have gotten busy.

But email is a good way to help those abandoned carts get active again. The trick is working out the timing of the email and the message must-includes, such as a clear statement about refunds. Want to discover how to craft those emails so they’re successful? Try the tips in this graphic.

Abandoned Cart Emails: Your Best Tips, Tricks, and Examples

The Savvy Marketer’s Guide to HTML Email Best Practices

Email isn’t just something that you can toss off and do in a minute or two. Today’s robust marketing programs include email that’s thoughtful and creative, that sets specific program goals—and meets them.

But far too many business people and communication experts take too little time with email. They copy and paste, or think that the point is just to send the email—not to send the email well. And to do that, learning how to write the email in HTML, and learning what those best practices are, can give you a leg up from your competitors.

For example, you have to understand that what you’re seeing in front of you on your email may not necessarily be what everyone sees—different platforms equal different formatting. Your job is to remove variances, as much as you can, and create consistency. This graphic detailing those email best practices that you can follow can help.

The Savvy Marketer’s Guide to HTML Email Best Practices

The 80/20 Rule for Email Marketers


There are many different ways to apply the 80/20 rule. The law states that roughly 80% of the effects come from 20% of the causes.

For email marketers, the rule applies quite obviously in some areas, and more subtly in others. Let’s take a look at some examples, and see what it means for those of you out there trying to do more with your email marketing programs.

80/20 Rule for Subscribers

In the past, email marketers used to run around telling everyone how many subscribers they had. It was as if the bigger the list, the more successful we would be. As if raw number of subscribers was the be all and end all of email.

We’ve advanced beyond that now, I hope. We are smart enough to know that it’s not the size of the list that matters, it’s the outcomes.

We measure outcomes in a number of ways – opens, clicks, engagement, and conversions. A successful email marketing strategy is one that engages more people and leads them to purchase.

Applying the 80/20 rule here is easy. 80% of your actions (opens, clicks, sales, etc.) are going to come from 20% of your subscribers. These are your most engaged prospects or customers.

This matters because it helps you understand and set priorities. While you might always chase new subscriber growth, you need to know those subscribers who are most likely to take action. They are the ones keeping your business alive, the ones driving all of the ROI on your email marketing campaigns. And the more you can design the program around them, the better off you will be.

80/20 Rules for Emails

Sophisticated email marketers are managing a number of different campaigns for their company. You may have a weekly newsletter list, a product announcement list, a press list, a customer loyalty campaign, an onboarding campaign, and an abandoned cart campaign. You might have even more.

And each of these lists/campaigns has a number of different emails tied to them. Even small or mid-sized companies might send more than 100 different kinds of emails over the course of a calendar year.

But will all of those emails impact the business equally? Obviously not.

It’s likely that 80% of all performance will be driven off of just 20% of those emails. And this matters to email marketers because it tells us where to focus and how to prioritize our time.

While it might be nice to spend the time and effort to redesign your email newsletter every few months, if it’s not driving sales or loyalty, your time might be better spent elsewhere. Focus on those emails that are most likely to boost performance and you’ll be rewarded for it with higher pay/more resources.

Other Uses of the 80/20 Rule

20% of the products or services that you offer will make up 80% of the total sales you get from email marketing.

Though you will constantly be testing, 80% of the overall lift in performance will come from the 20% of tests that you run that will actually matter.


Your time is valuable. It’s valuable to you and it’s valuable to your company. Make sure you are focusing on the right things by measuring outcomes and being aware of where your efforts will have the largest payoffs.

5 Simple Steps to Effective Email Personalization (Guest Post)

This is a guest post by Kimberly Maceda. Kimberly is a content writer for ActiveTrail. She writes for some top online marketing sites and blogging advice on email marketing and marketing automation.


Gone are the days when one-size-fits-all emails work. Customers today are more hooked on content and messages that appeal to their unique interests and individual needs. So if you are still blasting that one email to your entire list, it's time to stop and rethink your strategy.  

Personalization gives heart to your email. Because your email has a personal touch, customers won't feel like talking to a robot or an automated message.

Using customer data for email marketing personalization allows you to send relevant offers and content. This sends a message to your customers that you take time to know them on a deeper level, enabling you to establish a stronger relationship.

When this happens, everything else will follow. Your open rates, clicks, and sales will boost up. In fact, personalized emails can deliver up to 6 times higher transactional rates.

Level up your email marketing personalization with these best practices.

1. Understand your Customer Profile

It starts with how well you know your customers. Data helps you personalize your email marketing.

The problem here is that most email marketers stop gathering data after customers submit the sign-up form. If you want to up your personalization game, gather customer data in every chance you have and at every touchpoint.

For instance, you can send a survey email each time a customer purchases a product to know more about their interests and preferences. Purchase history can give you an idea of what product or service to offer them next time. You can also ask them to share their birthday with you so that you could send them gifts on their special day.

Your email marketing automation software can even help you identify which pages customers frequent on your website. This gives you a hint on what they are thinking of buying from you.

2. Use Data Analytics to Power Your Personalization Game

Wise marketers always look at data analytics to improve their email marketing campaigns. From time to time, check the analytics in your email automation software to see what your numbers have to say.

Your data can show you how well your email personalization tactics are performing. You can use it to determine which strategy is working and which is not. Once you see this, you would know which strategy to continue and which to stop.

3. Leverage your Email Marketing Automation Software

It's good to know all the features of your email automation software, so that you can maximize the opportunities from this technology.

Of course, you have your basics such as using the first name in the subject line and content. But since you are automating emails, setting up triggers should be one of the first things you must master.

Simply put, triggers are conditions that start automation when customers meet your pre-determined criteria. This way, you are sure that the emails you send are relevant and personalized as they are based on the actions of customers themselves.

In e-commerce, a trigger that sends an automated email reminder to customers who abandoned their shopping cart is basic. You can also set up a trigger that sends a welcome email to new subscribers or a thank you email each time a customer buys an item to confirm their purchase.

4. Innovate your List Segmentation Process

Personalization begins with proper email list segmentation. Compared to non-segmented campaigns, segmented emails can bring up to 14.32% higher open rate and 100.95% higher click-through rate.

Using your customer data, you can group contacts sharing similar characteristics, so you could send them targeted emails containing offers that appeal to their interests.

For instance, you can segment contacts such as gender and age to make it’s easier for you to send promos based on demographics. Segmenting contacts based on where they are on the buyer journey can help you warm up cold leads and push hot leads to finally make a purchase. Some businesses group their loyal customers in one email list to enable them to strengthen their loyalty program.

Your email list segmentation techniques are limitless. You just have to check your data to know how well you can create effective segmentation.

5. Continuously Test Your Email Campaigns

If you want your email marketing to keep on improving, then you must keep on testing.

To know how which email campaign can yield better open rates, test your email subject line. Test your CTAs for higher click-through rates. You can test almost anything in your email automation software. Just remember, always test with a goal in mind.

Testing can help you determine the personalization tactics that work to your contacts so that you can apply them to other email campaigns.

Email marketing personalization is a basic tactic, but many marketers still fail to do it. Follow these tips to give your email campaigns a personal touch that your customers deserve. But before you do, remember to pick the right email automation software that enables you to personalize your email marketing campaigns in advanced ways.