How to personalize email subject lines

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📝 Intro

Scientific evidence keeps evolving - as does people’s behavior - which is why it’s crucial to stay up to date with the latest research.

A previous study from 2018 by researchers at Stanford and University of Chicago found that including a person’s first name in an email subject line had powerful positive effects:

• Open rates increased 6-23%

• Clicks by 7-32%

• Unsubscribes fell 11-17%

Today, first name personalization in email subject lines is everywhere.

So researchers from Austria’s Johannes Kepler University Linz wondered whether the effect still holds, and tried to replicate the results.

They found that what works now has fundamentally changed. But not all is lost for email subject line personalization.

P.S.: We previously covered the 2018 research mentioned above as an Ariyh insight, recommending you use [First name] customization in your email subject lines. That insight has now been retired, as this new research displaces it.

I’m building Ariyh’s platform to be the place where you can find the most up-to-date scientific evidence in marketing at any time. There are over 230 insights now and it’s constantly growing. Make sure to always check the platform for the most up-to-date recommendations.

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Use creative and relevant subject line personalization to increase email open rates

Topics: Messaging & Copy
For: B2C. Can be tested for B2B
Research date: September 2023 
Universities: Johannes Kepler University Linz

📈 Recommendation

Stop personalizing email subject lines using the recipient’s first name (e.g. “Thomas, here’s today’s insight for you”), it doesn’t have a positive effect anymore.

You should instead use less common but relevant ways to personalize your emails. For example, mention a product the person bought and rated highly (e.g. “Because you liked [product]”), or use their surname (e.g. “Would you like to donate again, Ms. Smith?”).

Your emails will have higher performance (e.g. open rates, clicks) and results. 

🎓 Findings

• Personalizing the subject line in emails can lead to higher open rates, click-through rates (CTRs), and unsubscribe rates if the personalized elements are creative or uncommon, and relevant. The commonly used method of using a recipient’s first name does not have an effect anymore.

• As part of 2 experiments in Germany, researchers:

  • Emailed 3,521 university students about a career platform (“[First name], a successful start for your career”) and found that:

    • Those with their name in the subject line had an open rate of 56.9% vs those without it 58.5%. This difference was not statistically significant

    • There was no significant difference in clicks or unsubscribe rates

  • Emailed 3,700 local politicians asking them to complete a survey (“[Title and last name], how do you view digitalization in politics?”) and found that:

    • Open rates were 11.8% higher for emails including the politician's last name in the subject line (38.8% vs 34.7%)

    • There was no statistically significant difference in clicks or unsubscribes

🧠 Why it works

• Due to security and privacy concerns, we often react negatively to very personalized emails if we don’t see a clear fit between the promotion being emailed and the personal information that’s being used.

• We react well to personalization only if we have a high level of trust in a brand. Otherwise, we find them to be invasive and are less likely to click links in the emails.

• Our reactions to email personalization have evolved as the tactic has become more common and we’ve gotten more used to receiving emails personalized with common methods (e.g. first names).

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✋ Limitations

• The research was done exclusively in Germany, where a more formal way of addressing people (compared to English) might make participants less receptive to being addressed by their first name. The research about first names published in 2018 tested audiences globally, in South America, and with Stanford students in the US. It’s possible that using first names is not effective in German but still is in other languages and cultures.

• The research looked at a student sample for one experiment and politicians for another. Students are likely to be younger and more tech-savvy, leading to more exposure to online marketing, while politicians are likely to be older and less tech-savvy, with less exposure to email marketing.

🏢 Companies using this

• Many companies use first name personalization, especially when customers have already engaged with a brand, as the customers are less likely to have concerns about their information being shared with the company.

  • Delivery Hero uses someone’s first name in emails about their order (e.g. John, your order is on its way)

  • Alibaba is amongst those who use first names when recommending similar purchases.

• Others use other personalized messages in their subject lines to make their emails stand out, though it’s unclear which is more effective. These personalizations include:

  • Location-based (e.g. now delivering to New York)

  • Purchase-based (e.g. because you bought this dress)

  • Event-based (e.g. special gifts for your wedding anniversary)

Cosmetics company Sephora not only personalizes the subject line of their emails with first names but sends their emails on a personalized calendar, targeting shoppers on their birthday

⚡ Steps to implement

• The more value your email can provide, or relevant the personalization you offer is, the more likely it is to resonate:

  • Share special offers or related products to previous purchases (e.g. a travel site offering hotel information to a customer after they book a flight)

  • Share content or messaging based on audience interests. For example, if someone buys sports merchandise, you can target them with offers related to the team whose items they’ve bought, or use sports-related language (e.g. score the winning goal, touchdown)

  • Include relevant information, like geographic information (e.g. now opening in Greenwich Village)

  • Experiment with fun and creative (but relevant) personalization

🔍 Study type

Field experiments (3521 emails sent to university students and 3700 sent to local politicians)

📖 Research

Personalized subject lines in email marketing. Marketing Letters (September 2023).

🏫 Researchers

• Laurens Defau, Johannes Kepler University Linz

• Alexander Zauner, Johannes Kepler University Linz

Remember: This is a new scientific discovery. In the future it will probably be better understood and could even be proven wrong (that’s how science works). It may also not be generalizable to your situation. If it’s a risky change, always test it on a small scale before rolling it out widely.

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