Split testing (a.k.a A/B testing) shouldn't be reserved just when email campaign performance drops.
In email marketing, consistent testing is how you improve results over time — not fix problems after they've appeared.
A practical approach is to create a simple testing cycle: choose one element, test it, apply what you've learnt, then move on to the next.
Once you reach the end of your testing list, start again.
Every part of an effective email marketing campaign can be optimised, but it makes sense to begin with areas that are clearly underperforming, right?
What Should You Test First?
Almost every element in a marketing email can influence — and affect — results, including:
- Subject lines
- CTA wording and design
- Email layout and structure
- Send time and frequency
If you're not exactly sure where to start, focus on what directly impacts engagement.
Subject lines affect open rates.
CTAs affect click-throughs.
Improvements in these elements tend to deliver the most immediate return.
One Variable or Multiple?
Standard advice is to test one variable at a time. This makes it easier to attribute changes in performance to a single factor.
However, in practice, metrics are connected.
If an email is not opened, CTA performance becomes irrelevant.
This is why some marketers test subject lines and CTAs across different segments within the same email marketing campaign.
That said, complexity increases quickly.
For most teams, especially SMEs, keeping tests simple produces clearer and more reliable insights.
Why List Segmentation Matters?
Split testing only works when your audience is properly divided (segmented).
Sending different variations to separate segments of your email marketing list allows you to compare performance under similar conditions.
Without segmentation, results become quite tricky to interpret (unless you have a crystal ball or something) and may not reflect genuine subscriber preferences.
There's also a practical benefit. If a test performs poorly, only a portion of your audience is exposed to it — reducing the risk of disengagement or unsubscriptions.
Interpreting Results In Context
Not all performance changes come from your testing efforts.
External factors — seasonality, news cycles, economic conditions, even weather — can influence results.
For example, demand for seasonal products can shift engagement significantly during certain months.
Split testing helps reduce this noise because both versions are sent at the same time.
However, if you're testing across highly specific segments, external factors may still affect groups differently.
Interpretation should always consider context.
There's No Universal Benchmark
It's tempting to compare your results to industry averages, but in email marketing, "normal" performance varies widely.
Open rates and CTRs depend on:
- Your audience
- Your product or service
- Your pricing and positioning
- Timing and external conditions
The only meaningful benchmark is your own baseline.
The goal of split testing is simple: improve it.
A Practical Approach To Ongoing Testing
Rather than setting rigid targets, focus on incremental gains. Even small improvements in open rates or click-throughs compound over time across multiple campaigns.
A straightforward process looks like this:
- Identify one element to test
- Split your audience into comparable segments
- Run the test under identical conditions
- Apply the winning variation
- Move to the next variable
Consistency matters more than complexity.
The Takeaway
There are no fixed rules for split testing in email marketing — but there is a clear principle: test continuously.
Every email campaign is an opportunity to learn more about your audience.
Without testing, you rely on assumptions.
With it, you build an effective email marketing strategy based on real behaviour.
Over time, those small, data-led improvements are what separate average email campaigns from high-performing ones.
