What are the benefits of subject line A/B testing in email marketing?

Today, almost everyone has a device in their pocket. Businesses can no longer expect their customers to come to them. Instead, businesses need to reach customers wherever they are at any time. This usually means you will find them while they are looking at their phone. One of the key elements that signals to your audience that you understand the things that matter to them is the subject line of your emails. The best way to ensure that your message gets across is A/B testing each subject line for almost every email you send.

This brief guide will give you the building blocks for establishing an effective subject line A/B testing strategy.

How does A/B testing work in email marketing?
As the name implies, A/B testing is a process in email marketing to determine what brand messages can provide the best results. It is up to your business to define what ‘best results’ means, but for the purpose of this discussion, we can assume that the results wanted are some type of conversion: a click-through to the website for a purchase, a sign up to a webinar, or a newsletter subscription.  

There are many different types of A/B tests, some more complex than others. For example, you could test whether your subject line performs better or worse than a different subject line. You can also test whether sending an email on Mondays works better than Tuesdays or Thursdays. This discussion is focused solely on subject line A/B testing because subject lines are the most important part of your email marketing strategy since they’re the first interaction a customer has with your business messaging in their private inbox.

Subject Lines can make or break a campaign
Subject lines can make or break your chances of converting a lead. Every email campaign your company sends should have at least two subject lines and be delivered as an A/B test. Not only will this testing help you optimize your campaigns by helping you avoid putting all your eggs in one subject line basket, but you can review previous subject lines to see which ones have performed best and modify them to use them in campaigns to further refine results. 

Subject line effectiveness varies from industry to industry and campaign to campaign. It’s always worth trying different subject lines to find a style that works best for your type of campaigns.

Why should you use subject line A/B testing?
To get better conversions, of course, but there's another, deeper reason for using subject line A/B testing in your email marketing.

Most businesses live within their own bubble where internal assumptions about the business, the audience, the market, and everything associated with them is hardly ever challenged. A/B subject line testing helps you avoid groupthink via the simple method of testing multiple ideas about your company, your customer, and your market, via the emails you send regularly. It is a low cost tool for experimentation that can be measured and modified as you learn new information and incorporate it into your marketing messaging.

What is the structure of an effective subject line?
Subject line testing isn’t a random process. There is a structure to effective subject lines that can help you get started and build subject lines that are more likely to get past the spam filter and reach your customer’s inbox. 
Keeping your subject lines short is helpful. Keeping your message truthful is also helpful: baiting your customers with misleading or outright incorrect subject lines is the most certain way to get them to declare your emails as spam. 

The subject line that works can be a conversation opener for your audience, for example: 

1. A promise (It's Your Lucky Day! Take 17% Off Sitewide☘️)
2. A joke (Did You Know Why The Chicken Crossed The Road)
3. An invitation (How To Use MS Word - Easy)
4. A declaration (This Email Teaches You To Write)

Often, for algorithmic reasons, subject lines that include an emoji and a number have a better chance to get past the spam folder. Also, subject lines that have a capital on every word seem to work better.

The point of following the structure is to help you keep your message short, sharp and to the point. Remember, most people will be looking at these messages on their phone, so you have to assume that you only have, at most 5 words to get the message across. You can use more, of course, but whether they will be visible on the screen is debatable.

Naturally, the effectiveness of a shorter or longer message would be subject to - you guessed it - subject line testing.
This structure is meant to be a helpful scaffolding to begin your experiments. It would be irrational to talk about subject line testing, how it is individual to your business and audience, and then declare that this or that type of subject line will work for you. The only way to find out what works for you based on this structure is to do your own testing during your email campaigns.

What are effective subject lines?
While subject line testing has an obvious objective (increasing conversions from the email), focusing on just that one objective robs the strategy of additional value. Effective subject lines aren’t about your business, they are about the interests of your audience. A/B testing subject lines constantly allows you to probe, test, and confirm (or falsify) your assumptions about your audience, how your business is perceived in your market and how your audience perceives your business. This is an effective method for improving not only your email marketing, but your overall marketing content. Effective subject lines are the ones that reach your audience in a manner they think is best. To do that, it is good to know what your audience values about your product or service. 
 
What is the content of an effective subject line?
Once you decide to build on the structure mentioned above, you need to worry about what content you will test. Usually, this means testing what you think is important for your audience. You learn what is important for your audience in the easiest way: you ask them. 

If you’ve done an audience survey, you may glean from the response's words or themes that you can test in subject lines. You can set up a question in a pop up on the site, to try to sharpen customer interest in your products or services.
You can also do a list of your own assumptions about your audience and set them up as subject line tests to see how well your audience reacts to them. 

Nothing is easier than simply offering a discount with every email you send. The subject line that includes a discount, limited time offer, usually gets good results. But if you constantly tell your audience that your products are available at a discount, you may get them addicted to getting that message and they may not purchase again until they see it in their inbox. 

Subject line testing allows you to branch your message out by emphasizing the value of the products you sell to the audience. In the case of makeup, for example: Instead of offering 10% discount for makeup sales until Friday, you could  offer ``Here's a way to make your eyes shine” or “here’s makeup that doesn’t cause breakouts”. You could test all three subject lines to see which one gets the results that are closest to the discount offer, and continue to refine them over time.

If you're marketing a webinar to women in their 30s and 40s, you might want to experiment with different subject line variations like “Meetings this Week?” “Women in Business” or “Your Step-by-Step Guide to Success.” Different angles to the main proposition in the email give you the chance to see how your audience views your product and what they find valuable about it.

You can use your A/B testing plan as a way to learn what your audience values simply by testing multiple value propositions with every email campaign or automation you send.

Don’t forget the Preview Line
The subject line is not the only part of your message that your recipients will see. There’s also the Preview line. That’s the line that appears directly under the subject line in most inboxes. In subject  line testing, the preview line could remain the same in both A and B versions, however, you could also do a B version of the preview line to see if the message can be improved, particularly with more complex offerings, or with messaging that would be longer than 5 or 6 words just on the subject line.

One of the best ways to use the Preview line is as a continuation of the subject line. It can be used as a way to complete the thought that the subject line starts. For example:

Subject Line: “What’s Your Favorite Color?”
Preview Line: “Our fall selection is sure to have it”

The preview line can supplement what the subject line states, and act as the friendly invitation to act on the email right away. 

Subject Line: “This Friday: Learn Microsoft Automate”
Preview Line: “Automation to save time and hassle every day”

An effective subject line is always paired with a good, explanatory preview line.

What about the content of the email?
It’s important that the content of the email continues the message in the subject/preview line pairing. Sometimes, the subject line can be a motivator for the email content itself, but often it reflects the content of an existing message that, presumably, the customer will find valuable. The connection between the two should be firm and without ambiguity.

When can you stop doing subject line A/B testing?
As long as your business is alive and acquiring new customers, then subject line A/B testing adds value to your email marketing strategy. As your audience and your business changes, subject lines (and preview lines) are the first point of contact for your brand in a customer’s inbox. The more in-tune you are with what your audience values about your product or service, the better results you will get from your subject and preview lines, and so from your email campaign in general.

Test your subject lines to see what are the things your audience values about your product or service to create an effective marketing messaging strategy. Keep the content of your emails tightly focused and clearly related to your subject/preview lines pairing. 

A constant testing approach to your emails means you will avoid creating a monoculture of messages that your customers will learn to ignore over time. Keeping things fresh and your audience engaged are the best rewards of a successful subject line A/B testing strategy.