Email Testing: The Ultimate Guide

If you want to reach your customers with professional communication as a seller on bol.com, email testing is an essential step. Whether it's about order confirmations, promotional emails, or follow-ups after purchase - a well-tested email prevents your messages from ending up in the spam folder, looking bad on mobile, or missing crucial information. In this comprehensive article, you'll learn everything about email testing: from technical checks to content optimization.

Why is email testing so important for bol.com sellers?

Email is still one of the most powerful communication channels for e-commerce sellers. Research shows that email marketing averages a ROI of €36 per invested euro. But you only achieve these results if your emails actually arrive, are opened, and prompt the recipient to take action. Without thorough testing, you risk:

• Deliverability issues: emails that end up in the spam folder or don't arrive at all
• Display issues: an email that looks perfect in Gmail but is unreadable in Outlook
• Broken links: links that lead to 404 pages or show incorrect products
• Spelling mistakes and incorrect information: an unprofessional impression that damages your brand trust
• Personalization errors: variables that aren't filled in correctly, such as "Dear {first name}"

With the right testing approach, you avoid these problems and maximize the effectiveness of every email you send. Tools like the email campaign feature of Zoloo help you streamline this process.

The 7 essential steps for email testing

1. Test email sending

The first and most basic step is to send a test email to yourself. This sounds simple, but many sellers skip this step. Send the test email to at least three different email addresses: a Gmail account, an Outlook account, and possibly a business email address. This way, you check the display in the most used email clients.

2. Subject line check

The subject line determines whether your email is opened. Test different variants and pay attention to:

• Is the subject line not too long? (max 50-60 characters for optimal display on mobile)
• Does the subject line contain no spam trigger words like "FREE", "BUY NOW", or excessive use of capital letters?
• Is the preheader text set correctly and relevant?
• Does the subject line evoke curiosity or urgency?

3. Content and layout verification

Check the full content of your email for the following points:

• Spelling and grammar - use a tool like LanguageTool for Dutch texts
• Correct product information and prices
• Clear call-to-action buttons with the right links
• Consistent corporate design and branding
• Logical reading order and hierarchy

4. Links and buttons testing

Click on every link in your test email and check if it leads to the right page. Pay extra attention to dynamic links that can vary per recipient, such as personalized product recommendations or unique discount codes. Also, verify that UTM parameters are set correctly so you can measure campaign results.

5. Image check

Images are a common source of problems in emails. Check if all images load correctly, if the alt texts are present and descriptive (in case images are blocked), and if the file size is not too large. The total email size should preferably remain below 100 KB for fast loading times.

6. Variables and personalization testing

If you're using personalization in your emails, test whether all variables are replaced correctly. Send tests with different customer profiles to check if the name, order number, product name, and other dynamic fields are filled in correctly. Also, test the fallback behavior: what happens if a variable is empty?

7. Test mobile display

More than 60% of all emails are opened on a mobile device. So, always test your email on both desktop and mobile. Check if buttons are large enough to tap with a finger (at least 44×44 pixels), if the text is readable without zooming in, and if the layout adapts correctly to smaller screens.

Email testing: statistics and benchmarks for e-commerce

To understand how your email performance compares to the average, it's helpful to know the key benchmarks. The table below shows the average performance for e-commerce email campaigns in the Netherlands:

By regularly testing and comparing your results to these benchmarks, you can work on improvement in a targeted way. The Zoloo Sales Dashboard helps you measure the effect of your email campaigns on your sales results.

A/B testing: the scientific approach to email testing

A/B testing (also known as split testing) is the most reliable method to optimize your emails. You send two variants of the same email to a small part of your list and see which one performs better. You then send the winning variant to the rest of your list.

What can you A/B test?

• Subject line: short vs. long, with or without emoji, question vs. statement
• Sending time: morning vs. evening, weekdays vs. weekends
• Sender name: company name vs. personal name
• CTA button: color, text, position, size
• Content: long vs. short, with or without images
• Personalization: with name vs. generic, product recommendations vs. general content

Rules for reliable A/B tests

To draw valid conclusions from your A/B tests, follow these rules:

• Always test only one variable at a time
• Use a minimum sample size of 1000 recipients per variant
• Let the test run for at least 24 hours before choosing a winner
• Repeat successful tests to rule out coincidence
• Document your test results for future reference

Technical aspects of email testing

SPF, DKIM, and DMARC

Technical email authentication is crucial for deliverability. Check if your domain is correctly configured with:

• SPF (Sender Policy Framework): determines which servers are allowed to send emails on your domain's behalf
• DKIM (DomainKeys Identified Mail): adds a digital signature to your emails to prove authenticity
• DMARC (Domain-based Message Authentication): combines SPF and DKIM and gives instructions to receiving servers on what to do if authentication fails

Without these technical settings, there's a high chance your emails will be marked as spam, no matter how good your content is.

Inbox preview tools

There are various tools that allow you to test how your email looks in different email clients without having to send test emails to all those platforms. Popular options include Litmus, Email on Acid, and Mailtrap. These tools show previews for dozens of email clients and devices at once.

Checklist: testing your email before sending

Use this checklist every time you're about to launch an email campaign:

Common mistakes when testing emails

Even experienced marketers make mistakes when testing emails. Here are the most common pitfalls:

1. Only testing on desktop

Many sellers only check their test email on a desktop screen and forget about the mobile view. Since most emails are opened on mobile, this is a crucial mistake. Always test on at least two devices.

2. Not performing a spam check

Your email might be perfectly formatted but still end up in the spam folder. Always perform a spam score check using tools like Mail Tester or GlockApps. A spam score above 5 (on a scale of 10) is a red flag.

3. Attachments or images that are too large

Heavy emails are more likely to be blocked by email providers and load slowly on mobile networks. Optimize your images and avoid attachments - use links to download pages instead.

4. Forgetting to test the unsubscribe link

A non-working unsubscribe link is not only annoying for the recipient but also a violation of AVG/GDPR legislation. Always test if the unsubscribe link works correctly and if the recipient is actually removed from the list.

5. No fallback for blocked images

Many email clients block images by default. Make sure your email is still understandable and usable without images by using good alt texts and a text-based layout as a basis.

Testing emails for specific e-commerce scenarios

Order confirmations

Test if the order number, product details, shipping address, and expected delivery date are displayed correctly. These transactional emails often have the highest open rates (up to 70%) and are a great opportunity to add extra value with cross-sell recommendations.

Abandoned cart emails

Check if the correct products are shown, if prices are up-to-date, and if the return link leads to the correct shopping cart. These emails can recover up to 10% of lost revenue if set up correctly.

Review requests

Test the timing (not too soon after delivery), the link to the review form, and the display of the purchased product. Positive reviews on bol.com are essential for your sales position.

Conclusion

Thoroughly testing emails is not a luxury, but a necessity for every serious bol.com seller. By systematically testing - from technical deliverability to content quality and mobile display - you ensure that your emails reach the inbox, are opened, and generate conversions. Start with the checklist from this article and gradually build a testing process that is standard for every campaign. With tools like the email campaign feature of Zoloo, you make testing and optimizing your emails easier than ever.