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Email marketers have spent years following the identical advice: use power words, personalize subject lines, avoid ALL CAPS, and keep punctuation to a minimum. A brand new study suggests a few of those rules could also be hurting performance as an alternative of helping it.
Researchers on the University of Helsinki analyzed 31,812 marketing email subject lines sent a combined 4.6 billion times. Their goal was to find out which long-standing copywriting conventions hold up when tested at scale. The results challenge several familiar “best practices” and reinforce the worth of testing assumptions as an alternative of counting on conventional wisdom.
Promotional language isn’t all the time persuasive
The study’s biggest surprise could also be its findings on so-called power words.
Terms like free, exclusive, today, flash, and save have appeared in email marketing advice for years. They’re often presented as reliable ways to extend opens. In the study, subject lines containing these words generated significantly lower open rates than those without them.
It’s likely that these words are so familiar that they not stand out. In crowded inboxes, straightforward language may earn more attention than predictable marketing phrases.
ALL CAPS also worked against marketers. Subject lines containing fully capitalized words reduced open rates by about 3.3%, suggesting subscribers proceed to reply negatively to what appears like shouting.
The research also confirmed that shorter subject lines consistently performed higher. Each additional character had a small negative effect on open rates, reinforcing the worth of concise writing.
Some rules deserve testing
Some findings were less definitive, but still useful.
Personalization produced a modest improvement in open rates. The researchers also noted that previous studies reached conflicting conclusions depending on the audience and stage of the buying journey. Their advice is to check whether personalization improves results on your subscribers moderately than assume it all the time will.
Punctuation also produced an unexpected result. Subject lines containing a single exclamation point increased open rates by nearly 4%. The finding supports using emphasis sparingly while avoiding the excessive punctuation commonly related to spam.
The researchers also found that slight departures from conventional writing, including creative punctuation or formatting, were related to higher open rates. Carefully breaking convention may help an email stand out in a crowded inbox, provided readability and professionalism remain intact.
What marketers should test
The findings also offer useful guidance for teams using AI to write down email campaigns.
Many AI writing tools generate subject lines based on these copywriting best practices. As a result, asking AI to provide “high-converting” subject lines stuffed with urgency and promotional language can automate outdated habits.
The search engine optimization toolkit you understand, plus the AI visibility data you wish.
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It’s higher to make use of AI to generate variations, then test the assumptions behind them. Compare a simple subject line against one crammed with power words. Test personalization against a generic version. Try concise copy against something longer. The objective is to learn which writing principles hold true on your audience.
Marketing folklore isn’t the identical as evidence
The larger lesson extends beyond email.
Marketing has amassed a long time of rules, formulas, and best practices that are repeated in conference sessions, agency presentations, and online guides. Some survive because they consistently work. Others survive because they’ve been repeated often enough to develop into accepted wisdom.
Marketers who treat established advice as a hypothesis, test it with their audiences, and measure the outcomes have a stronger foundation for deciding which practices to maintain of their playbook.
The delightfully named study, “Do You Want $150 for FREE? Measuring the effect of language on marketing email open rates,” was published within the journal Ampersand, and could be downloaded here.
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