Email marketing remains one of the most powerful tools in a marketer's toolkit. Despite the rise of social media and other digital channels, email consistently delivers the highest ROI, with an average return of £33 for every £1 spent. But here's the catch — even the most perfectly written email won't deliver results if it ends up in the spam folder or is never opened.
Testing your email before sending is critical to ensuring your message reaches its intended audience. But most marketers either don’t know how to test their emails properly or don’t realize how much email testing can improve their overall performance. In this comprehensive guide, we’ll cover:
- Why email testing is essential
- Common deliverability issues
- Best tools for testing your email
- How to interpret your test results
- How to fix issues that hurt deliverability
- A checklist to help you improve your email performance immediately
By the end of this guide, you’ll know exactly how to test your emails, improve deliverability, and boost your email marketing ROI.
Why Testing Your Emails Is Essential
Think of email deliverability as the foundation of your email marketing strategy. You could craft the most compelling subject line and provide incredible value in the body — but if the email never reaches your recipient’s inbox, it’s wasted effort.
According to recent research:
- 15% of marketing emails never reach the recipient’s inbox.
- Up to 69% of recipients mark emails as spam based on the subject line alone.
- Nearly 30% of recipients will stop opening emails from a brand after one bad experience.
Testing helps you prevent these issues and improve your chances of success by addressing key problems before you send.
The Three Core Elements of Email Deliverability
Deliverability depends on three key factors:
-
Sender Reputation
ISPs (like Gmail and Outlook) assign a score to your sending domain and IP address based on factors like open rates, spam complaints, and bounce rates. A poor reputation reduces your chances of reaching the inbox. -
Email Content
Certain words, phrases, or formatting issues can trigger spam filters. Even something as simple as using too many images or failing to include an unsubscribe link can hurt deliverability. -
Authentication
Properly configuring SPF, DKIM, and DMARC records tells ISPs that your email is legitimate and helps prevent spoofing and phishing.
Common Issues That Hurt Email Deliverability
Testing your emails helps you catch the following issues before they damage your email reputation:
1. Spam Triggers in Subject Lines
Spam filters are sensitive to certain words and phrases. Using terms like “Free,” “Guaranteed,” or “No Risk” in your subject line can land you in the spam folder.
2. Broken or Improper Code
HTML formatting errors can cause your email to appear broken or distorted on different devices and email clients.
3. Unclear Sender Information
If the "From" field is misleading or inconsistent, it can trigger spam complaints. Always use a recognizable sender name and domain.
4. Poor Text-to-Image Ratio
Emails that are too image-heavy can appear suspicious to spam filters. A balanced email should contain around 60% text and 40% images.
5. Too Many Links
Including too many links (or shortened URLs) can make your email look like spam. Keep it simple with one or two key CTAs.
6. Missing Unsubscribe Link
An email without an unsubscribe link can be marked as spam. Make it easy for recipients to opt out if they choose to.
Best Tools for Testing Your Emails
Testing your email deliverability is easier than ever thanks to several powerful tools. Here are the top options:
1. Mail Tester – Fast and Free
Mail Tester allows you to send a test email and get an immediate score based on key factors like spam triggers, blacklists, and content issues. It also provides actionable feedback to help you fix issues.
How to Use Mail Tester:
- Go to Mail Tester.
- Send your email to the test email address provided.
- Get an immediate deliverability score and improvement suggestions
My score pictured below btw 👍😉
2. GlockApps – Detailed Inbox Placement Testing
GlockApps tests how your email is received by different ISPs and mail clients. It also provides detailed reports on how to fix any issues.
3. Litmus – Design and Compatibility Checking
Litmus allows you to preview your email across different devices and platforms. You can see how it will look on Gmail, Outlook, Apple Mail, and more.
4. MXToolbox – Blacklist and Authentication Testing
MXToolbox checks if your domain or IP address is listed on any major blacklists. It also tests your SPF, DKIM, and DMARC settings.
How to Interpret and Act on Test Results
Testing is only useful if you know how to act on the results. Here’s how to handle common test outcomes:
Low Score on Mail Tester- Review the specific issues identified.
- Fix any spam trigger words, broken links, or formatting issues.
- Resend and test again.
Emails Landing in Spam on GlockApps
- Check your SPF, DKIM, and DMARC records.
- Test different subject lines and content formats.
- Try removing excessive links or shortening the length of your email.
Poor Design on Litmus
- Adjust your HTML and CSS code.
- Test on multiple devices to ensure consistent formatting.
- Keep your design mobile-friendly.
Blacklisted on MXToolbox
- Contact the listing service and request removal.
- Stop sending emails from the blacklisted IP or domain.
- Improve email engagement to rebuild your reputation.
Actionable Tips to Improve Your Email Deliverability
Here’s what you can do right now to improve your email deliverability:
✅ Set up SPF, DKIM, and DMARC records properly.
✅ Keep your email list clean — remove inactive or unresponsive addresses.
✅ Avoid spam trigger words like "free," "guaranteed," or "act now."
✅ Use a familiar sender name and email address.
✅ Include a plain-text version of your email.
✅ Make your emails mobile-friendly with responsive design.
✅ Keep a balanced text-to-image ratio (around 60/40).
✅ Include an easy-to-find unsubscribe link.
Email Testing Checklist
Before you send your next email, go through this checklist to maximize your chances of reaching the inbox:
✔️ Send a test email to Mail Tester and aim for a score above 9/10.
✔️ Check email formatting and compatibility using Litmus.
✔️ Confirm that your SPF, DKIM, and DMARC settings are correct.
✔️ Remove any spammy language from the subject line.
✔️ Keep the email under 100 KB to avoid clipping.
✔️ Include a visible unsubscribe link.
✔️ Test CTA links to make sure they work properly.
✔️ Review sender name and email address consistency.
✔️ Remove broken HTML and excessive formatting.
✔️ Test on multiple devices and platforms.
Start Sending with Confidence
Testing your email doesn’t take long — but the results can make or break your campaign. By following these steps and using tools like Mail Tester, you can avoid the spam folder, improve open rates, and increase conversions.
Need help improving your email strategy? Secret Source Marketing Specialists can help you craft high-performing email campaigns that get results. Get in touch today to take your email marketing to the next level.