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The Best Subject Line Is...

Posted on 4.28.2015

Return Path is helping email marketers achieve better subject lines.

A new study by the data solutions provider is shedding light on several widely held beliefs about consumer preferences and behavior when it comes to email. For starters, the study shows that “clickbait” subject lines, such as “You won’t believe this shocking secret…” are very successful at capturing Web traffic but are among the least effective of the 10 subject lines examined. Additional data found that the use of “Secret of” resulted in an 8.69 percent decrease in read rates compared to messages containing similar content sent under different subject lines. Conversely, the word “shocking” resulted in a 1.22 percent decrease in read rates.

The study, which analyzed more than 9 million messages sent by prominent global brands to more than 2 million consumers, also found that that benefit-based subject lines featuring superlatives like “fastest” were better at getting consumers’ attention, resulting in a 5.3 percent higher read rate than comparable messages sent under different subject lines. Moreover, read rates for urgency-based subject lines, like “limited time,” “last chance” and “expiring” were also higher.

The most surprising part of the study, however, found that two classes of value-based subject lines resulted in unexpectedly low performance: those promoting prices and discounts. For instance, subject lines containing keywords that identified discounts, like “discount,” “save,” “sales” and “clearance” resulted in lower read rates. Additionally, pricing references like “free,” dollar signs and percentages also coincided with lower read rates than comparable messages with different subject lines.

Lastly, Return Path found that subject line length does not make much of a difference. While subject lines that ran longer than 100 characters correlated to the lowest read rates (8.8 percent), subject lines with between 91 and 100 characters were among the best performing in the study (15.1 percent). Plus, the most common range of 40 to 49 characters (used in 25 percent of all messages) coincided with some of the lowest average read rates (11.6 percent). Return Path notes that read rates appeared to be better for slightly longer and slightly shorter subject lines, yet states that correlation is clearly random.

“Subject line optimization presents one of the clearest opportunities to apply advanced analytics toward understanding and significantly increasing marketing performance,” said Return Path President George Bilbrey. “By analyzing extremely large data sets collected across the entire email ecosystem, based on how real subscribers engage with messages sent from thousands of trusted brands, marketers can quickly, efficiently, and confidently test subject lines to ensure that their messages are read by as many people as possible. As this study demonstrates, the results are often surprising, frequently questioning or even invalidating long-held best practices.”

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