Why email subject line testing makes a huge difference to your email campaigns

By: Richard Michie

Attention is the name of the game for email marketing. Email subject line testing will make a massive difference in how your email campaigns perform.

Email plays a key role in our marketing strategy. We’ve been testing our subject lines for a while now, to try and beat our “banker”, which we’ve been using for over a year.

For our most recent email newsletter, we were convinced we had a new winner. It was timely, to the point, amusing and intriguing. The only way to be sure was to test the subject line.

It’s all too easy to be over-enamoured with your subject line and not even consider alternatives.

The key to email subject line testing is to change just one thing.

This way, you can be sure your test is valid. Change too many test elements at one time, and you can’t be sure which change had an effect.

What type of email content works best?

It’s important to bear in mind the type of email content we are sending out in our monthly newsletter. Rather than a hard sell, we send out a collection of stories, based around marketing, with a few pieces of our own content added in too.

Our aim is to educate our customers and show we are marketing experts.

If your emails are sales led, then you’ll need a very focused approach to get your email opened in a very crowded inbox.

What email subject line did we test?

  • Our banker email subject line is – I think you’ll find this interesting
  • We tested it against – Welcome back to the office, bedroom, kitchen table

The email we tested was sent in very early January, so the test subject line felt like it was timely, lent into how people might be feeling, and was ‘stand out’ enough that we’d gain more opens.

Amongst the team, some preferred the test subject and thought it may outperform our banker email subject.

The only way to know for sure, was to run email subject line testing.

At the time, our email database stood at around 2,500, all ‘clean’ contacts, with all opt-outs removed. The deliverability of our emails is around 97% which is really healthy.

We use Campaign Monitor for all our email marketing. One of the reasons we use it, is its really robust testing tools.

Email subject line testing allows us to send the same email content with different subject lines, to a random sample of contacts, for 1 hour. The system then analyses open rates and clicks, and identifies a winner, before sending the email to the remaining contacts.

We chose to send the A/B email test to 10% of our contacts, and ensured that the email went out on the same day and time we usually email, to ensure these factors didn’t skew the results we received.

While watching the test live, the results showed no discernible difference at all, and if we were feeling especially impatient, we might have made the call to manually stop the test. As it turned out, it was worth waiting until the email test was complete, as there was a stark difference in open rates right at the end, which made a huge impact on our decision making.

Email subject line testing results

By running email subject line testing, and selecting Version A as the winner, Campaign Monitor estimated that we received an additional:

  • 521 opens – a 204% increase
  • 77 more clicks – a 64% increase

The results of the test made a huge difference to the final results of our email marketing campaign. If we had just gone with our gut and used our new email subject line – ditching our banker – we just wouldn’t have reached as many people.

And more importantly, we wouldn’t know why.

We’ll continue to test subject lines, as you never know when you find that slight edge that makes a big difference.

If you’d like to learn more about our email subject line testing approach, email marketing process, or how we can help you with your outbound marketing, get in touch.

Interested in speaking to The Optimists?

Right from the beginning of our time working with The Marketing Optimist, they’ve taken the time and effort to get to understand Sharp Consultancy as a business and not just a client. We’ve seen a huge increase in the effectiveness of our social media strategy, particularly on Linkedin and we’re delighted with the impact it’s had on the business.

Jamie Caulfield

Regional Director, Sharp Consultancy

It was a pleasure to work with The Marketing Optimist on this project. It felt like a true collaborative effort on the day and they made the interviewee's feel at ease whilst talking about their journey on our RISE programme. The final video was professional and engaging, we have received great feedback around the quality and creativity of the case study. Including the video in our presentation made it come to life, with real humans sharing their stories, so thank you to the Marketing Optimist!

Hannah Prole

Impact Manager, Better Connect Limited

Case Studies


Marketing for Local Government

Moresby Hall Hotel

Hotel Rebranding

Sharp Consultancy

B2B Social Media for recruitment

The Edit LDN

Managing advanced eCommerce SEO

Better Connect

Digital PR and video production for events

Tango Networks

Marketing support for a global telecoms business

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