Email marketing rewards people who keep testing. Small improvements to subject lines, layouts and offers don’t look like much on their own, but they add up over a year of sends.

This is where A/B testing comes in. It lets you find out what works for your readers, rather than relying on what works for someone else’s.

What Is A/B Testing?

A/B testing, sometimes called split testing, is the practice of comparing two or more versions of individual components within your email marketing campaigns, and measuring the impact each of these has on campaign performance.

The results from A/B tests give you a quantifiable way to figure out which design elements, writing styles, subject line structures, etc. work best for your audience.

How Do A/B Email Marketing Tests Work?

Many ESPs offer the ability to split test components of your campaign. This is generally limited to basics like subject line and content. But there are plenty of other tests you can run, which we’ll cover in a minute.

By testing different versions of your content or subject line, you can see which performs best on the metric you care about: clicks, conversions or revenue. Open rate used to be the default, but since Apple Mail Privacy Protection made a large share of opens automatic, clicks are a much more reliable way to pick a winner.

Most ESPs offer the ability to run an A/B test by sending a small segment of your list the various versions of your campaign. For example, 10% will receive version one, and 10% will receive version two. After a period of time, the winning version is sent to the remaining 80%.

Over time, that adds up to noticeably better results than never testing at all.

Send both versions at the same time where you can. If you send one on a Monday and the other on a Friday, you’re testing the day as well as your change, and you can’t tell which made the difference.

As a general rule of thumb, A/B testing should only be run on one variable at a time. If you change more than one thing at a time it can be difficult to know which variable is responsible for the results. This is in contrast to multivariate testing, which is used to test multiple combinations of variables. Multivariate testing is much more complex, and requires a very substantial list size to make successful, so we’ll leave that for another day.

Below are 14 email marketing tests worth running. Not all of them will make a difference for your list, but most are quick to set up.

1. Subject Line

Try testing the length of your subject lines, capitalization, tone, emojis, specific keywords and punctuation. There’s a lot to test here. Judge subject line tests on clicks rather than opens, for the Apple Mail reason above.

Your subject line is also a good place to test personalization, like including the subscriber’s first name, to see whether your readers respond to it.

Also try experimenting with using second person pronouns such as “you” instead of “them” to see how your audience responds to a more conversational tone.

2. Preview Text

The preview text is the short teaser text that you see alongside or below your subject line in the inbox. This can be every bit as influential as the subject line on your campaign’s open rates as it’s visible before the subscriber even opens your message.

Use this text snippet to write persuasive copy that entices users to click to read more.

You can experiment with the length of preview text, the keywords used, punctuation and emojis. You can think of the preview text as a way to pre-sell your content and qualify your readers. It’s a sub-header. Your second chance at grabbing attention, so make the most of it.

3. Sender Name

The sender name is important but something you probably don’t want to change too often. It’s as much a part of your branding as it is another variable, so try to decide early on how you would like to be perceived.

Having said that, you can use this variable to experiment with a sender name that is easily recognized and promotes trust.

For example, your regular campaigns may have the sender name “ABC”, but your monthly deals campaigns may perform best if they’re sent from the name “ABC Deals” (because subscribers would know what content to expect before opening, perhaps resulting in lower unsubscribe rates).

As another example, you may want to try sending your re-engagement campaigns from the name of your CEO, rather than your brand name, and craft the email as a personal message to the subscriber, rather than a generic email blast. This may result in more people staying engaged with your list over the long-run.

These are all tests worth running.

4. Send Times

Day parting and scheduling can have a profound impact on your open rates. It’s worth looking at where your readers are and testing accordingly. Do they prefer to receive your emails at the weekend? In the morning, or in the evening? Are conversions higher on a Monday compared to a Friday?

Many ESPs will allow you to send campaigns in the user’s specific time zone, but if this is not possible you may want to consider segmenting your users along these lines.

Optimal send times are worth revisiting every so often, even if you’ve tested them before, because readers’ habits change. Be careful with send time tests based on opens, since Apple Mail records opens when the email arrives, not when it’s read.

5. Delay Periods

You can also experiment with different delay periods between automated sequences to figure out if a longer delay leads to higher open rates and vice versa.

You may receive more sales if your autoresponder sequence is sent out daily or weekly, rather than every other day. Or maybe you consistently see highest performance on a Saturday, so all of your important sales-based autoresponders should therefore be sent on a Saturday.

6. Copy

The words you use in your campaigns can change the way people engage with your content and can make or break your click-through rate. Your copy should flow naturally from one line to the next, and persuade the reader to take action.

Experiment with short vs. long copy, tone of voice, and the soft vs. hard sell approach. Try to apply different copywriting formulas to see what effect each one has on your conversion rate. Remember, each audience is different, and will respond to different copywriting styles.

7. Content Type

The type of content you send is also worth testing. Does featuring a single product lead to higher conversions than a list of ten products? Do your subscribers react better to promotional material, or material aimed at entertaining/educating them?

8. Headlines

While testing the subject line aims to increase your open rate, striking the right balance for the headline displayed at the top of your email template is just as important. Test different variations of attention grabbing headlines and try out personalization, along with bold statements, fonts and colors.

9. Primarily Text vs. Primarily Image

Test using text-centric vs image-centric content to give varying degrees of weight to your content and can influence the conversion and engagement rates for your campaign.

Experiment with images and GIFs, as well as above-the-fold and below-the-fold placements for your graphical content. You can also test UX design elements in your nav bar, header and footer and monitor the results in your stats.

10. Resend the Same vs Resend a Different Message

The type of content you use also comes into play when deciding whether to resend the same message, or send a different message to your subscriber file.

Many ESPs offer the ability to resend the same message to subscribers who didn’t open it the first time around. Bear in mind that Apple Mail users often show as “opened” whether they read it or not, so a resend to non-openers misses some people and reaches others twice. “Didn’t click” is a more reliable filter. In some cases, a resend works well. In other cases, it might be best to craft a different message entirely, perhaps a better deal, or a different deal, rather than regurgitating the first deal that didn’t strike a chord last time.

11. HTML Email vs Plain Text

One of the most overlooked email marketing tests is HTML email vs plain text, and the results can be surprising. While plain text emails are not as visually engaging as HTML they are also less distracting, giving your content greater focus in the email.

A popular choice for marketers is the hybrid email approach. This format mimics plain text but allows for more advanced tracking and analytics and gives you more control over the formatting.

Plain text emails may also result in better engagement in reactivation campaigns as they come across as more personal and less a piece of marketing.

Some senders also find plain text lands in the inbox more reliably, especially if their HTML template is heavy or badly coded, though your reputation and engagement matter far more than format for email deliverability.

12. Segmentation

Segmentation offers a golden opportunity to send relevant and targeted content to your subscriber file. Testing how different segments of your list react to different campaigns can help you to make informed decisions about which content leads to the highest engagement.

For example, you could segment your list into subscribers who have made a purchase in the last 30 days, and subscribers who haven’t. You can then test which offers resonate best with each of those segments, allowing for a much more targeted email marketing strategy.

13. Offers

Testing different offers helps to keep your message fresh in the minds of your readers, and can boost your conversion rate. Does offering “20% off” result in higher conversion than “Save $25”, for instance?

You can also try out different strategies such as urgency tactics and countdown timers and monitor the results on your engagement stats to see which ideas lead to the highest conversion rates.

14. CTAs

All other things being equal, your CTA can have a huge impact on clicks. Try using different styles of buttons, text, copy, size, and colors, along with first and second person messaging to see which performs the best.

Even something as simple as the wording or placement of a CTA can make a noticeable difference to clicks.

Which Email Marketing Tests Will You Be Running?

A/B testing should be a regular part of how you work, not a one-off project. Plenty of tests won’t show a meaningful difference, and that’s useful to know too. The ones that do will add up over time.

Keep a simple record of what you tested and what happened. A year of small, written-down tests on your own list is worth more than any benchmark report.