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The 10 Best (and Worst) Performing Words in Email Subject Lines

by Ayaz Nanji  |  
August 10, 2015

If you want to boost engagement with your email campaigns, it helps to say "thank you" in the subject line, according to a recent report from Adestra.

The report was based on data from more than 3 billion attempted email sends that were part of 125,000 global campaigns sent by brands in four industries (retail/B2C, conferences/events, media/publishing, and B2B). The researchers selected the 300 most popular single words, characters, and two-word phrases and then looked at the relative lift or decay of each term versus the average.

As the report notes, the results only provide a "broad interpretation of the causal effects of individual words"; that is, they are a general overview of average performance and the terms won’t always work for every brand.

Overall, email subject lines that include the words "thank you" have the highest above-average engagement levels (+62%)—perhaps because many automated, transactional messages include this phrase, such as email receipts sent by brands after customers complete online purchases.

Subject lines that separate topics with pipes (e.g., "Sale now on | New lines added | Win trip to Dubai | Share your pics with #summer2015rules") also perform significantly above average (+47%).

Timeliness also tends to work well in email subject lines, with words such as "bulletin" (+32%), breaking (+27%), and "order today" (+27%) all boosting engagement.

Not surprisingly, mundane words that make reading feel like work hurt engagement levels with email subject lines.

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Ayaz Nanji is an independent digital strategist and a co-founder of ICW Content, a marketing agency specializing in content creation for brands and businesses. He is also a research writer for MarketingProfs. He has worked for Google/YouTube, the Travel Channel, AOL, and the New York Times.

LinkedIn: Ayaz Nanji

Twitter: @ayaznanji

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  • by Elizabeth Mon Aug 10, 2015 via web

    I feel this is slightly skewed. I feel that the "Thank you" and "Thanks" email subject lines are probably confirmations e.g. "Thank you for your purchase" from airplane tickets, to shopping orders, to event registrations, or even contests and promotions "thank you for entering" - and everyone opens those. I don't foresee people opening a monthly newsletter email with the title "Thank you for reading our newsletter", it's not really the same thing.

  • by Ayaz Nanji Mon Aug 10, 2015 via web

    Hi Elizabeth. Thanks for the comment! You're completely right, I tried to spell that out a bit in the fourth paragraph of the post but may not have conveyed it fully -- a large part of why "thank you" emails perform so well is because they're often automated responses for buying something, etc., and so are more likely to be opened.

  • by Udita Tue Aug 11, 2015 via web

    I've seen fairly good open rates with "Good Morning/Evening, first-name". I believe the subject line should be personal, rather than a "50% off on coffee mugs!" to improve open rate. Sometimes, a simply "Hey!" can do wonders. I've also noticed another trend - till about 2-3 years back, a sense of urgency in subject lines made people open emails but that is steadily declining. I think that's primarily because every business now bombards people with promos, discounts and coupon codes that shout "ONLY FOR TODAY!" "RUSH NOW!" etc. and it has become too much of an everyday phenomenon.

  • by Dan Pearson Sun Aug 16, 2015 via mobile

    Tell me something I don't know. That's what I suggest as the best approach for writing subject lines. That precious few words really perform the same function as a newspaper headline. Doesn't one scan his or her inbox deciding to open or not to open based on the promise of that subject line? Shouldn't it tell you just enough to make you want to know more?
    So, the discipline I recommend is this. Try to provide a four or five word prťcis of what is to follow. For example: RESPONDERS GET FREE STUFF. or VIEWERS LEARN GOLF SECRETS., or WORD GURU WOWS MARKETERS. ( No self promotion intended.)
    Assume that your email recipients are intelligent but busy; skeptical and curious. Give them the truth with just a bit of spin.

  • by Francoise Mon Aug 17, 2015 via web

    It all sounds very B2C and I would love to see a similar ad for B2B.
    Several terms in the bottom ten ranking graph might include the results of the few B2B used in that study. And while they are low compared to a sales offer, within their own field they might be ranking fairly high.

  • by Paul Morello Tue Aug 18, 2015 via web

    Thanks for the insight.

    Its interesting to see what people respond to when they go through their emails. Since the word "Thank-you" is still seen favorably, I suppose its possible to use it to your advantage. Perhaps in a job search or reaching out to someone.

  • by Bill Thu Aug 20, 2015 via web

    We definitely theorize that effectiveness of email subject lines is very dependent on the eye, mood, and needs of the reader (e.g. context variables) vs. just keywords. The context variables probably end up with a direct and actionable phrasing of a statement / question mix (i.e. "Sorry we couldn't help you. Are you still using our 'resource'?"). When sent to right customer, recent experiences have shown email open rates %3E75% for some targeting groups when the context variables are right. In those particular cases, on a sample of around 1,000 customers, a negative context tone email achieved the level of open rates we didn't believe were achievable. In addition, it was interesting to see that some customers actually never opened emails, but responded with follow-on actions that were the targets for the messaging.

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