What CMOs Need to Know About Email Subject Lines

Parry Malm

The CMO of 2021 has a lot on their shoulders. 

As the most senior marketer in every business right now, the task of the CMO has become taller than ever. The relationship between brand and consumer is shifting in new and unexpected ways, and the pressure to have all the answers in a rapidly evolving marketing landscape is being felt across the marketing world.

The proliferation of digital marketing channels, already decades in the making, and the need to service all these marketing channels with effective, engaging content has kicked into high gear.

But, in the race to maximize your brand’s presence on emerging digital marketing channels, it is crucial to ensure that all fundamental bases are covered as effectively as possible.

The old normal

One of the greatest revelations in recent weeks has been the resurgence of humble email as the critical marketing channel in 2020. For marketers, the ‘old normal’ has made quite the impact and arguably is even more powerful than ever before. And yet, is the power of this channel even on the radar of most CMOs?

Every consumer touchpoint is a branded moment. This immutable truth of marketing is just as true in the email inbox as it is anywhere. Email is your brand’s most direct pathway to the consciousness of its audience, free from interference/monetization by third parties and their individual agendas (which may not necessarily align with yours).

Over-delegation could destroy value

Relegating your brand’s email subject line copy to an afterthought or leaving it to junior members of your email marketing team could be a costly error and you potentially risk losing out on revenue and impacting campaign potential. The value of the email channel and subject line copy’s importance to success on this channel demand more.

With global email open rates hovering somewhere around the 20% mark, ensuring that your brand’s subject line copy stands out from the crowd and engages your audience as effectively as possible will be crucial in the uncertain weeks and months to come. And, whether you know it or not, the humble (and oft overlooked) email subject line is the surest path to accomplishing that lofty and important goal.   

Trust the science

Taking a science-based approach to your brand’s email subject line language is no longer a “nice to have”. It’s now a marketing imperative at the highest level. With that in mind, here are 5 science-based email subject line tips every CMO should take note of as 2021 begins… 

Anxiety-inducing marketing 

Brands have been using anxiety-inducing tactics/language to pressure consumers to buy for some time now. The experience of booking a flight/hotel online, for example, has in many cases become an exercise in anxiety and discomfort for consumers. 

Consumer data compiled by Phrasee and Vitreous world indicates that a full 68% of consumers in the UK and US would not buy from a company that targets negative emotions like stress and anxiety in its marketing. During a time of heightened sensitivity like the one we currently find ourselves in, avoiding such questionable tactics will likely become even more critical to audience engagement.  

Raising the bar on subject line copy

As Warren Buffet once famously said, “If the reason for doing something is that everyone else is doing it, it’s not a good enough reason.” As the world’s inboxes fill up with issue-of-the-day email subject line language, the question of whether to make this part of your brand’s subject line copy strategy is indeed an important one. 

The key question for brands: is this relevant? And. More importantly, will anyone care?

I recently received an email from a restaurant in New York I ate at in 2011. The subject line read “It’s safe to eat here again”. Thing is, I live 4,000 miles away from that particular restaurant. Is this effective use of subject line copy? 

Building effective subject line copy isn’t about keywords. It’s about signaling that you’re making an offer based on a ubiquitous retail moment. 

In extensive split tests during the Black Friday and Christmas seasons on of 2019, for example, Phrasee found that email subject lines which included the words “Black Friday” and “Christmas” underperformed compared to those which didn’t in almost 50% of cases.

If your competitors are attempting to capitalize on this situation, there may be a competitive advantage in holding back and keeping your messaging on-brand and avoiding social change subject line copy altogether.

The discounting race to the bottom 

Does discount-based email subject line copy work? In the short-term, it can (and often does). However, over time, such an approach devalues your brand and its products. If you constantly bombard your email audience with discount-driven email subject line copy, what message are you really sending? Why would any consumer pay full price for your products again? 


This might seem a trivial issue, but does an email subject line’s length have an appreciable impact on its performance? Despite the proliferation of blog posts outlining an “ideal” or “optimal” subject line length, actual data measured and tracked at scale suggests that it doesn’t.  

To focus on a subject line’s length is to focus on the wrong part of the problem. Getting your brand messaging right and identifying the language that has an impact on audience engagement – while a much tougher problem to solve – yields much more robust results.  


Applying advanced technology to a problem as seemingly insignificant as the humble email subject line may seem like overkill. However, email subject lines consistently appear near the top of the list for consumers’ decisions about whether or not to open an email (second only to sender name).

Ensuring that your email subject line copy is on-brand and effective has a deep effect on how your brand’s emails are perceived by your target audience. Send enough cheesy email subject line copy, and you’re likely to wind up with a customer who stops paying attention, or, worse still, relegates your emails to the dreaded spam folder. 

Why this should matter at CMO level

The relationships between brands and their consumers have changed. Tech (like AI) can help you protect yours. Email subject lines may appear to be a small part of this, but they are important to the way your audience perceives your brand and its marketing.  

Re-engaging and focusing on the areas that deliver the biggest boost in email marketing performance and amplify your brand messaging will offer big dividends in 2021. Now is the time to re-evaluate your digital marketing strategies and re-engage with this underutilized but highly lucrative marketing channel.

Parry Malm is the CEO and co-founder of Phrasee, which empowers brands with the most advanced AI-Powered Copywriting technology. Parry has been working with brands to optimize marketing results for almost 20 years. He is an expert on digital marketing and combines this expertise with a track record in computer science, statistics, and commercializing artificial intelligence. He was named Tech Entrepreneur of the year at 2016’s UK Business Awards and Phrasee was recognized by CB Insights as 2017’s Most Innovative AI Company, having also been awarded Best New Business at the UK Business Awards in 2016. He has contributed evidence at the Houses of Parliament in London about how the UK can become a global artificial intelligence leader.

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