Plain vs. HTML Email Test: Which Email Increased Revenue by 303.08%?

Plain vs. HTML email? Which one is the best? Will sending a plain text emails to email subscribers for this IT exam website work better, or are the HTML emails more suitable? We decided to test. In this case study you will learn that in some cases and for certain industries a plain email is more suitable.

What we tested
We tested the weekly newsletter to find out which version, plain vs. HTML, is more suitable for this client. So we split the email subscriber database and the same day we sent plain emails to one half, and the HTML email to the second half of the subscribers.

Plain Email                                                                             HTML email


Test background
–    we sent over 100,000 emails on the same day at the same hour
–    we split the email subscriber database equally 50:50
–    all emails we tagged for tracking in Google Analytics
–    we used the same subject line
–    in both cases we directed visitors to the same landing pages
–    we used the same ‘10% off’ offer in both emails

Test results
A week later after we sent the email campaign out, we analysed the results. To our surprise, the difference between both emails was really significant. In the screenshot below you can see that the plain email increased revenue by 303.08% and visits to the site by 194.51%. Clearly, for this type of product the plain email seems to be more suitable.

(click on the image to enlarge)

Here is some speculation on the possible causes of the test outcome.
•    Many email clients have images disabled by default. Possibly for this reason the HTML email didn’t performed as well as it could.
•    The plain email was more personal (included customer support representative name, plus contact details) and as it loaded in each email client without any problem, so it got read more.

Want to experience similar results and pay only when we increase your conversion rate? To contact regarding conversion optimization call +44 (0)20 7617 7848 or contact me at

Jan Petrovic
I have 9 Years of Tremendous Experience as web analyst and Senior Conversion Specialist. I have worked on optimisation project for the second-largest store retailer in the USA (the company is also a component of the S&P 500 Index), as well as for a well-known USA fashion retailer with over 380 stores nationwide. Over the course of my career I have achieved many INSANE improvements on our client’s websites, sometimes by applying best practices, another time from findings I made during conversion audits and sometimes thinking out of the box. For one of them I have even received an award in 2012 from WhichTestOne, where after testing different emails and parts of email message we increased revenue by 303.08%. What might also interest you is the fact that my average conversion improvement is 19% and my success rate is 70%. Basically, I’m VERY GOOD at what I do thanks to my Can Do Attitude to find solutions to given problems & Experience in this field.
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