How Currys Achieved a 56% Open Rate Increase by Optimising Email Subject Lines in Real-time

Midway through 2021, electricals company Dixons Carphone announced that it would be merging its four technology and retail businesses – Currys PC World, Dixons, Carphone Warehouse, and Team Knowhow – under the Currys brand name.

Announced in May of last year, the merging of the four brands was complete by October. In its wake, the newly-unified Currys decided to take another look at the way it approaches personalization across the business, and improve its approach to personalised communications.

“We were doing really good personalization on a channel-by-channel level,” explains Saul Lopes, Head of CRM at Currys plc. “[But] we found the opportunity to actually take a step back and look at end-to-end personalization moments – how could we give customers a complete personalized experience, end-to-end?”

This thought process gave rise to a new collaboration with AI-powered copywriting platform Phrasee, with whom Currys had already been partnering for several years, and led to Currys becoming the first brand to experiment with Phrasee’s new real-time language optimization technology, Phrasee X.

In this article we will discuss how Currys came to implement real-time optimization of its abandoned basket email subject lines, how the technology works and what results it gained, and why marketers shouldn’t view personalization as an end in and of itself – but why it can be a powerful solution to certain business problems.

The importance of language

When Currys initiated its end-to-end personalization project, the team set out to isolate ten moments that had the greatest customer value.

“We’re really, really focused on: what are the ten moments that have the most customer value? And how we can improve the way we personalize not just on email, but on the web, call centers, in a retail shop, et cetera, et cetera – throughout all of our channels,” explains Lopes. “That was a really good exercise that we did across the business, and out of it came these opportunities.”

The team highlighted moments such as, “When we do fail, how do we better say I’m sorry? How do we better communicate that message and recover that customer?” and, “If a customer is hunting for a product, how can we better assist that sale?” They looked at ways to treat VIP customers differently, and how to reconnect customers who had gone “completely cold”.

They then began to drill down deeper into the “I’m hunting for something” use case and consider what it meant for things like CRM communications; for a customer who went into the My Account section of the website; for a customer who went into a store.

“By doing this personalization exercise, what I felt is that we sometimes forget the importance of language within these use cases,” says Lopes. “Generally, when we talk about personalization, what’s the very first thing that comes to everyone’s minds? It’s, ‘Okay, how are we going to personalize the product on the webpage? How are we going to create some piece of content? How am I going to create a new video?’

“But when we started chatting with Phrasee, it kind of opened my eyes to – why not start with the language first? How can we personalize our language so that we can better communicate with customers and better engage?”

Prior to this, Currys’ collaboration with Phrasee had mostly been focused on its broadcast messages and re-engaging its mass communications. However, with Phrasee’s real-time technology, Phrasee X, Currys identified an opportunity to focus on communications that were “targeted and timely”, and personalize them on a one-to-one level. The idea came about at one of Currys’ regular catch-ups with Phrasee, and the two teams alighted on abandoned basket emails as a “quick win” for trialing Phrasee X in Currys’ marketing communications.

“They’re the highest revenue, because they’re so timely, and they hit the customer right at the best point,” says Lopes. “So, we decided, ‘Let’s start here first, and then we can think about the other channels where we can migrate this type of technology and this type of thinking.’

“We had a really great opportunity to trial … language that is completely personalized and customized to each one of our customers,” Lopes goes on. “The language that we’re using right now is completely unique on a customer-by-customer level because we added a lot of data variables within that language; but not only that, it’s also optimized by Phrasee in real-time. And in the future, we can leverage that language and leverage those learnings to the other channels.

“We sometimes think about personalization as something a lot bigger and grander – it just wasn’t something I was [initially] considering. But we stumbled on it, and just found such a great opportunity.”

How real-time subject line optimization works

Real-time optimization of email subject lines sounds fantastically sophisticated, but how does the technology work in practice?

“The best way to think about it is like this: back in the day, before Phrasee X existed, we had a lot of customers – including the good folk at Currys – who would use Phrasee in the broadcast sense; a standard test and deploy style of campaign,” says Phrasee’s Parry Malm.

“The problem with that is that when your goal is to optimize the overall ROI on a campaign-to-campaign basis, there are some inherent inefficiencies in your methodology – and we’ve recognized this for some time.”

Malm references a multi-variant optimization methodology called the “multi-armed bandit” methodology – a more complex version of A/B testing in which marketers have different proportions of different variants operating alongside each other. “Much like a horse race – if you have ten horses running down the track at Ascot, then you invest more in the horse at the front, and you invest less in the horse at the back. And over time, we can add in more horses to the race, so we’re constantly doing the champion versus challenger thing,” he explains. So, for email subject line optimization, substitute ‘horses’ with ‘email subject line variants’.

However, assessing performance in the context of email marketing presents some unprecedented challenges. “The delivery of response metrics – opens, clicks, conversions – are not uniform,” says Malm. “You can’t just roll out a multi-armed bandit and hope for the best. We had to do a huge amount of research and engineering work to make it feasible.”

On top of this basic methodology is the real-time language optimization that makes Phrasee X unique. “We’ve got all of these different variants running simultaneously, being optimized in the statistically most efficient way possible; but we can then in real-time amend, augment and inject a new language into that competition,” Malm explains. “So, you’re constantly learning and constantly improving as time goes on.

“That’s why the abandoned basket example is such a nice example. What a layperson would do is they’d say, “Let’s just run an experiment, find the best one, and stick to that for the rest of time.” But time stops for no one. We cannot rest on our laurels and assume that what worked yesterday will work tomorrow.”

At its heart, the methodology used by Phrasee X is a multi-variant test, but instead of the test being carried out at a single moment in time, it’s carried out continuously, in what Malm refers to as “a very statistically efficient manner”.

“We purpose-built this AI to make the choices that are statistically most likely to maximize ROI,” he says. “It’s very important that we don’t apply pre-conceived notions about how an experiment could be run. The methodology is not fixed – depending on the circumstances of the given experiment, Phrasee’s AI might augment existing language that is working well, or it might interject new, never-seen-before language into the mix.”

“I think when we started off the tests, we went through 40 or 50 different variants until we actually landed on the top three,” recalls Lopes. “And it’s still optimizing. We’re never stopping.”

He also emphasizes that the AI doesn’t make choices about language without any human input or oversight. “Every week or every two weeks, Phrasee will come back to us and say, “Hey, why don’t we try these ones out?”

“And it isn’t Phrasee introducing brand-new language without any human oversight or control – I know that that can sound a little bit scary for many. It’s Phrasee coming to us and saying, “We’ve looked at your language, and we’ve looked at your algorithms; we think we should put these new ten subject lines within the pot and test”. Of course, we have to go through business standards, we have to see if everything is above-board; then we input them into the pot, and we optimize. And then you’ll see, three or four weeks later, three or four have left the pot and are no longer important, and we start seeing the winning subject line on the top.

“It’s something that we’re constantly changing and reviewing. There’s always that element of human review of this language.”

The Phrasee tool also learns based on the language that a brand is already using in their communications, in order to closely replicate the brand’s voice. In other words, it’s following a path laid down by human copywriters, and then optimizing the language of each subject line based on performance, and using this to learn about what works.

“The way that the performance optimization system works is that it learns from past behavior to project onto the future while bringing in things that it’s not sure about,” says Malm. “By bringing in all this uncertainty in conjunction with past actions, you can actually create a very strong, highly accurate model, which can take on the ambiguity that happens in marketplaces and react very, very quickly. That’s what makes it inherently powerful.

“One more thing to bear in mind is that the more uses Phrasee has and the more language it tests out on a customer-by-customer basis, the more data points there are from which it can draw conclusions to project forward. So, there’s a certain network effect that stands out from heavy use.”

“So luckily, our three years’ worth of data and learnings really helped us to start high when we introduced it!” adds Lopes.

The results

Upon implementing Phrasee X across Currys’ cart abandonment emails, the team began to see “immediate results in terms of our open rates going up,” in Lopes’ words.

“We implemented it, and two or three days later we started seeing all of the Phrasee subject lines going up, and the human subject lines starting to go down, down, down,” he says. “It was really interesting to see in real-time, seeing our human control, and seeing all the alternatives that Phrasee was getting – and arriving at more or less our winner one, which was actually the one that was the most personalized.

“We personalized on the brand the customer was researching on; we referred to the price; for credit customers, we’d refer to the monthly price; and Phrasee learned all of this by itself, and was able to improve from our human subject line, which was, ‘Oops! Did you leave something in your basket?’

“That was very interesting to see in real-time, and see week-by-week how certain ones were going higher, certain ones were going lower, then we’d inject a few more, then we’d inject a few more… And it’s quite incredible that we got an improvement on something that has a very high bar. The engagement on these types of communications – we’re talking about open rates of 50, 60% already. And even on that, we were able to increase the engagement.”

A graph showing how quickly open rates began to climb once the Currys team implemented real-time subject line optimization on their abandoned basket emails.

A couple of months on from implementation, the team was seeing an overall increase in open rates of 57%, with double the amount of traffic coming to the Currys website, and a 9% improvement on conversion when compared with the human subject line. All of this led to an additional £2.5 million in yearly incremental online revenue for Currys.

Lopes reflects on how such a simple change – optimizing an email subject line (albeit in a technologically sophisticated way) – was able to bring about such impactful results. “We just personalized one sentence,” he says. “I constantly go back to it, and I think to myself, ‘Here am I, spending months and months of my life trying to do so much more complex and hard stuff … and hereby just changing a sentence, I was able to increase conversion by 9%. So that was a big, ‘Wow’.

“We sometimes get so hyped up in the data that we have, the data that we don’t have, on complex use cases and complex activations, that we forget the low-hanging fruit that’s right in front of our faces.”

“If you think about it, we’re all consumers here,” adds Malm. “Though we may not realize it, we’re all impacted on a daily basis by things as simple as a subject line in an inbox, or a strapline on an ad somewhere – little simple things like that.

“People can spend weeks and months trying to create this huge, intellectually pure, academically sound system that has all these bells and whistles – but if you’re not memorable, if you’re not noticeable, if you don’t get that subject line right – then it’s a big waste of time.”

This is not to say, of course, that marketers should focus exclusively on quick wins or that it’s never worth carrying out more complex marketing activations – but it’s important not to overlook the simple, fundamental things.

“It’s all a balancing act,” says Lopes. “My boss says this many times – in retail especially, you have to have “the big mo”, which is “momentum”. And I think quick wins and improvements like this give you that momentum that you need in order to invest on the bigger projects, on the higher-cost projects. By having all of these really good stories to start off with, you gain that momentum internally to be able to invest in things that are a little bit more complex and harder to do.”

I ask whether any brand could benefit from implementing technology like Phrasee’s and if they can, what might be holding them back from making use of it.

At present, Phrasee’s product suite is focused on enterprise-rate B2C customers like Currys, but otherwise, Lopes and Malm believe that there isn’t any reason why more brands couldn’t make use of this technology. “I sometimes think, ‘What are people waiting for?’” says Lopes. “It’s such an easy part of tech – they’re taking the complexity away.

“I know it can sometimes sound a little bit scary – ‘Oh, AI, what does that mean? Do I have a robot writing my copy?’ I think there is still those types of ideas. But what it is, is optimizing an existing touchpoint, an existing communication, an existing CRM strategy, and optimizing that language in order to say it better.

“It’s not creating the touchpoint or even the main content message – it’s not deciding that. It’s just deciding, ‘Okay, this communication has this objective; the current human language is this. How can we better optimize this language so that it communicates better to customers, and drives better ROI and conversion?’”

Personalization is not a destination

The importance of personalization is such a talked-about subject within marketing, with practitioners constantly discussing how to “do personalization”, how to carry it out more effectively, how to personalize at scale, what the future of personalisation will be, and much more besides. However, both Malm and Lopes emphasize that personalization shouldn’t be an end in and of itself.

“I don’t think personalization as a pursuit is important,” says Malm. “Ultimately, results are the most important thing. Now, often personalization for a specific purpose is the most effective way to optimize that end goal – but not always.”

He uses the example of a 30-second Superbowl ad, widely considered to be one of the most effective forms of advertising in the world – and which is fundamentally unpersonalized. “There are points in time where personalization should absolutely not be used, and marketers cannot – and should not – aspire to personalize everything.

“There are very specific and very powerful use cases for personalization – for example, personalizing abandoned basket messaging makes perfect sense. People are deep in the buying cycle; they need the extra prompts to go through to actual conversion. Hyper-personalizing that makes sense.

“But marketers should not aspire to personalize everything, because that’s not how marketing works. They should aspire to identify the specific use cases where personalization can be most effective, double down on those, and then focus on how to optimise their top-level messaging for the mass market.”

“Especially in marketing, personalization is sometimes used as a destination – ‘We want to be personalized,’” adds Lopes. “It’s like a train station, where you arrive – ‘Oh hey, look at us, we’re a personalized company!’ You sometimes see it as a company objective: personalization.

“But [Currys] kind of flipped that around – we focused first on, ‘What are the business problems we’re trying to solve? And is personalization a good solution to solve that business problem?’ For example, a big business problem might be, ‘How do we retain our most loyal customers?’ Maybe if we do a few more touchpoints, if we personalize a little bit better, if we give them visibility across our business and give them special treatment – then, we’re able to save them.

“I always like to start with a business problem first and ask if personalization is a good solution. I think that’s really important, because the word ‘personalization’ is bandied around everywhere, and as Parry said, it’s not the answer for everything.”

Speaking of destinations, where do Phrasee and Currys plan to go next with their partnership? One area that Currys is currently looking at is its program for helping customers to make better use of their newly-purchased tech. “We do have a really well-structured welcome program for our customers where we help them better use the tech that they just bought; so it’d be really interesting to use Phrasee, and Phrasee X technology, to improve that customer journey that’s completely experience-led and service-led,” Lopes says.

“Another area that we’re also looking at is end-of-product life cycle; so, if a washing machine is seven years old, if a TV is seven years old, that’s a long time ago that you engaged with us – so, how can we use Phrasee, and how can we use Phrasee X, to get that saliency and get the message out there of reactivating with Currys after a long purchase cycle?

“We’re really working on an end of product lifecycle program where we can reactivate customers and upgrade their tech to greener and more environmentally friendly products.”

“We’re always working with Saul, and Saul’s team, to find new applications and new use cases,” adds Malm. “The great thing about Phrasee’s customers is that we’re always pushing them, and they’re always pushing us. That’s why the technology – in terms of capabilities – has advanced so quickly, and why Phrasee as a business has grown so much in the last few years.”