Email A/B Testing for Improved Campaign Performance

Home » Blog » Email A/B Testing in 2025: Best Practices, Examples, and Winning Strategies

Email A/B testing is one of the most effective ways to improve email campaign performance. In 2025, when subscribers are overwhelmed with daily promotions, newsletters, and updates, A/B testing helps marketers make data-backed decisions that lead to better engagement and higher conversions.

Contents

What Is Email A/B Testing?
Why A/B Testing Matters in 2025
What You Can A/B Test in Email Campaigns
Real-World Example: Testing Subject Lines
How to Run a Proper A/B Test
Recommended A/B Testing Tools
A/B Testing Mistakes to Avoid
Advanced A/B Testing: Campaign Flows and Automation
How Long to Run Your A/B Test
How to Read and Apply Results
Real Case: Grammarly’s A/B Button Test
3 Quick A/B Testing Tips That Work
References

This article explains what email A/B testing is, why it matters, how to do it properly, and the most impactful elements to test—supported by the latest accurate data and research.

What Is Email A/B Testing?

Email A/B testing, also known as split testing, is the process of sending two versions of an email to small segments of your audience to determine which performs better. Once a winner is identified—based on metrics like open rate, click-through rate (CTR), or conversions—the winning version is sent to the rest of the list (Mailchimp, 2024).

Why A/B Testing Matters in 2025

Email marketing is still a high-return digital channel. According to the 2024 benchmark report by Campaign Monitor, email continues to generate an average ROI of $42 for every $1 spent. However, only 39% of marketers run regular A/B tests, even though those who do report:

28% higher open rates
33% higher click-through rates
21% higher conversion rates
(Campaign Monitor, 2024)

In an increasingly competitive inbox environment, small improvements driven by A/B testing can lead to big gains.

What You Can A/B Test in Email Campaigns

You can test nearly every element of an email. Some of the most valuable A/B testing areas include:

Subject Line
This directly influences open rates. According to Klaviyo (2025), testing subject line tone, urgency, personalization, or length can improve open rates by up to 26%.
From Name
Some subscribers open more emails when they recognize the sender as a person rather than a brand (Mailchimp, 2024).
Send Time
Testing morning vs. afternoon or weekday vs. weekend can help you find your audience’s active times (Moosend, 2024).
Email Copy
Short-form vs. long-form content affects CTR and engagement. Test different copy styles or content structures.
CTA (Call-to-Action)
Try “Buy Now” vs. “Get Your Deal” or different button colors and placements.
Images vs. No Images
Some audiences respond better to plain-text emails. Others prefer visual layouts.
Design and Layout
Mobile-friendly layouts or single-column emails often perform better, especially for mobile readers (Litmus, 2025).
Personalization
Including the subscriber’s name or previous activity can boost response (Klaviyo, 2025).

Real-World Example: Testing Subject Lines

Omnisend (2024) reported a test where a brand used two subject lines:

A: “Your Favorite Is Back in Stock”
B: “Your Favorite Is Back 🎉”

Version B, which included an emoji, increased the open rate by 13% and boosted CTR by 9%, showing that even a small change can impact results significantly.

How to Run a Proper A/B Test

Here’s a simple guide to running an effective email A/B test:

Step 1: Choose One Variable to Test
To get clear results, test only one element at a time—such as the subject line. Testing multiple changes at once makes it hard to know what caused the difference (Mailchimp, 2024).

Step 2: Set a Clear Goal
Pick a single performance metric you want to improve:

Open rate = test subject line or sender name
Click rate = test CTA, images, or copy
Conversions = test offer, design, or landing page

Step 3: Select Your Sample Size
Most platforms allow you to test a percentage of your list—e.g., 20% gets version A, another 20% gets version B. After a set time, the winning version goes to the remaining 60%.

Step 4: Choose a Testing Duration
Wait at least 24 hours to gather reliable data. Don’t stop the test too early—emails are often opened hours after delivery (Litmus, 2025).

Step 5: Analyze the Results
Look at key metrics like open rate, CTR, bounce rate, and unsubscribes. Choose the version with better performance based on your goal.

Recommended A/B Testing Tools

Most major email marketing platforms have built-in A/B testing features. Here are top tools for 2025:

Tool	Best For	Link
Mailchimp	Beginners and SMBs	Mailchimp
ActiveCampaign	Automation and advanced targeting	ActiveCampaign
Brevo (Sendinblue)	Cost-effective A/B features	Brevo
Moosend	Visual A/B testing	Moosend
Klaviyo	E-commerce automation	Klaviyo

These platforms also support send-time optimization, dynamic content, and re-sending to non-openers.

A/B Testing Mistakes to Avoid

Here are common errors marketers make—and how to avoid them:

Testing multiple things at once
Only test one variable to get clear data.
Using too small a sample
Small tests lead to unreliable conclusions. Use at least 100 contacts per group.
Declaring a winner too early
Let the test run at least 24 hours before checking results.
Not learning from outcomes
Use what you learn to improve future campaigns, even if the results are close.
Not repeating tests
A one-time test won’t give lasting answers. Audience behavior can change.

Advanced A/B Testing: Campaign Flows and Automation

A/B testing doesn’t have to stop at single emails. Many platforms allow you to test email sequences, drip campaigns, or workflow variations. For example:

Test email delay times in a welcome series (1 day vs. 3 days)
Compare different onboarding messages based on user type
Run split paths within automation to test design, offers, or tone

According to Litmus (2025), companies that test automation flows see a 21% increase in user activation and a 15% reduction in churn.

How Long to Run Your A/B Test

Run tests long enough to collect statistically significant data. For best results:

Wait a minimum of 24 hours
Get at least 100–300 opens or clicks per variation
Don’t run tests over holidays or unusual days unless relevant

Use significance calculators (like the one from AB Test Guide) to see if your results are meaningful.

How to Read and Apply Results

Don’t just look at the highest number. Review these:

Open rate = success of subject line or sender name
Click rate = content or CTA effectiveness
Unsubscribe rate = negative reaction
Conversion rate = ROI

Apply what works to future campaigns. Build a database of A/B test outcomes over time to guide your strategy.

Real Case: Grammarly’s A/B Button Test

Grammarly tested two CTA buttons in an email:

A: “Upgrade Now”
B: “Make Your Writing Stronger”

Version B delivered a 17% higher CTR, showing the power of benefit-driven language over generic commands (Klaviyo, 2025).

Top Testing Ideas by Industry

Industry	What to Test
E-commerce	Discounts vs. free shipping, CTA buttons, product images
SaaS	Demo CTA copy, onboarding steps, feature vs. benefit focus
Nonprofits	Emotional vs. statistical appeals, CTA phrasing (“Donate” vs. “Help a Child”)
Education	Webinar invites, testimonial content, video vs. text
Events	Reminder frequency, speaker bio formats, countdown timers

3 Quick A/B Testing Tips That Work

Use curiosity or urgency in subject lines
Subject lines with urgency can boost open rates by up to 22% (Campaign Monitor, 2024).
Make CTA benefit-focused
“Get Your Free Guide” works better than “Click Here.”
Re-test winners over time
What works today might lose impact in 3 months. Always re-validate top performers.

Note

Email A/B testing is one of the simplest, most powerful tools in digital marketing. By making small changes—and measuring the results—you can consistently improve open rates, clicks, and conversions.

In 2025, don’t rely on gut feelings. Let the data guide your decisions. Start by testing subject lines, then expand to layout, timing, and automation flows. Over time, you’ll build smarter campaigns and deliver better results for your business.

Start testing. Learn what works. And keep improving.