Why Testing Your Email Marketing in Mailchimp Matters More Than Ever

One of the most powerful — and most overlooked — advantages of Mailchimp is its ability to help you test your email marketing efforts. With features like A/B split testing and multivariate testing, Mailchimp makes it easy to learn what actually resonates with your audience instead of relying on assumptions.

I often find myself having interesting and very beneficial conversations with clients about what to test:
Which subject lines perform best? What type of content should we use — text, stories, images, products? When is the best time to reach customers?

And the truth is simple: not all audiences behave the same. Even two similar companies can see drastically different results. That's why we test.

Why Testing Is Essential

Testing helps you move from guessing to knowing.

By experimenting with different subject lines, content formats, images, call-to-actions, or send times, you learn:

• What gets your audience to open

• What motivates them to click

• What drives them to purchase

These insights become incredibly valuable, because once you discover what works, you can repeat it — and scale it.

Using Mailchimp's Automated Testing Features

With larger audiences, we automate the testing process and let Mailchimp do much of the work for us.

Here's how it typically works:

1. For each campaign, Mailchimp sends 10–20% of the audience a handful of variations (subject lines or content differences).

2. Mailchimp measures the winning version based on the success criteria we define.

3. After a set amount of time, the best-performing version is automatically sent to the remaining audience.

This automated approach allows us to test continuously without adding extra manual workload — and the performance lift is often significant.

Defining Success Criteria

Success looks different from campaign to campaign, but the most common goals include:

• Highest open rate (for subject line tests)

• Most clicks (for content and layout tests)

• Highest revenue (when e-commerce data is connected)

What surprises many clients is how unpredictable results can be. Even as a seasoned Mailchimp expert, I'm still surprised at times. A subject line I expect to win sometimes performs worse than a simple alternative. A content variation I think is too bold sometimes ends up driving double the clicks.

That's why we test — because audiences behave according to their own preferences, not ours.

Testing Inside Customer Journeys & Automations

Setting up automations in Mailchimp is straightforward, but designing the paths inside them can be challenging. Automations are usually built around our best assumptions:

• How many emails should be sent?

• How far apart?

• What content works best for new vs. returning customers?

• Should we use storytelling, a product-heavy message, or a combination?

To avoid relying solely on assumptions, I often recommend sending a small segment of contacts down a parallel path. This allows us to test alternative:

• Subject lines

• Email content

• Number of emails

• Timing of messages

Over time, these insights help refine your automations so they deliver better engagement and more revenue.

Stay Curious — and Keep Testing

It's easy to fall into routines. We all have our day-to-day tasks, and it's tempting to repeat what feels safe because we know "it kind of works."

But what if you could improve your open rate, click-through rate, or even your sales by 5–10% — simply by trying something different?

These improvements are absolutely within reach. I see them regularly when clients begin testing systematically.

A small tweak in timing…
A different content structure…
A new approach to subject lines…
A revised automation path…

These changes can compound and deliver meaningful business results.

Final Thoughts

Mailchimp gives you incredibly valuable tools to understand your audience better — if you use them. Whether you are sending one-off campaigns or designing advanced automations, testing should be part of your ongoing workflow.

The most important lesson is this:
Stay curious. Question your assumptions. Test the ideas you're unsure about — and even the ones you feel certain about.

Your audience will tell you what works. All you need to do is listen to the data.

Need help testing your marketing efforts in Mailchimp?

Frequently Asked Questions: Testing Email Marketing in Mailchimp

What is A/B split testing in Mailchimp?

A/B split testing in Mailchimp allows you to send two or more variations of an email to a small portion of your audience. Mailchimp then measures which version performs best based on a defined success metric and automatically sends the winning version to the remaining contacts.

What can I test in Mailchimp emails?

You can test a wide range of elements, including:

• Subject lines

• Sender name

• Email content (text, stories, images, products)

• Call-to-action buttons

• Send time and delivery timing

The key is to test one hypothesis at a time unless you are running a multivariate test.

What is multivariate testing, and when should I use it?

Multivariate testing allows you to test multiple elements at once and find the best-performing combination. It's especially useful for larger audiences where you want to optimize subject lines, layouts, and content blocks simultaneously.

How large does my audience need to be for testing to work?

For meaningful results, your audience should be large enough to distribute traffic across variations. As a rule of thumb:

• A/B testing works well with smaller audiences

• Multivariate testing requires larger audiences to deliver reliable insights

Mailchimp will guide you if your audience size is too small for a chosen test.

How much of my audience should be used for testing?

Typically, 10–20% of the audience is used for testing variations. The remaining contacts receive the winning version after the evaluation period. The exact percentage depends on audience size and campaign goals.

What success criteria can I choose for my tests?

Success criteria can be defined per campaign and usually include:

• Highest open rate

• Most clicks

• Highest revenue (when e-commerce tracking is enabled)

Choosing the right success metric ensures the test aligns with your campaign objective.

Can testing be automated in Mailchimp?

Yes. With larger audiences, testing can be fully automated. Mailchimp can automatically evaluate results and send the winning version without manual intervention, making testing scalable and efficient.

Can I test inside Mailchimp automations and customer journeys?

Absolutely. You can design parallel paths within automations to test different subject lines, content styles, send frequency, or timing. This is one of the most effective ways to optimize long-term performance.

Why do test results sometimes surprise even experienced marketers?

Because not all audiences behave the same. What works for one brand—or even one campaign—may not work for another. Testing removes assumptions and replaces them with real audience behavior.

How often should I test my email campaigns?

Ideally, testing should be ongoing. Audiences evolve, preferences change, and what works today may not perform as well tomorrow. Continuous testing leads to steady improvements over time.

Is testing really worth the effort?

Yes. Even small improvements—like a 5–10% increase in opens, clicks, or orders—can have a significant impact on long-term revenue and engagement. Testing helps you unlock those gains without increasing send volume.

More insights from a Mailchimp Expert