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There’s a lot of debate about the impact (or lack thereof) of subject line length in email marketing. The most important determinant of an email open may in fact be the sender, and research has also shown that preview panes are important. But with new data [download page] coming along from Yes Lifecycle Marketing (YLM), it’s worth noting that shorter subject lines seemed to have the most success in Q2.

Specifically, subject lines with a character count of 1-20 averaged an open rate of 18.5% (compared to less than 15% for those with higher character counts), a click-to-open rate of almost 13%) compared to less than 9% for longer subject lines, and a unique click rate twice as high as the longer subject lines.

Presumably, though, subject lines don’t have an impact on click rates, so open rates are the real variable that they could potentially influence. Even on that point, Yes Lifecycle Marketing acknowledges that there are many variables at play that combine to affect open rates, ranging from personalization to triggers. Indeed, triggered emails – which have far higher response rates than business-as-usual emails – accounted for 45% of shorter subject lines. So it’s possible that the higher open rates for shorter subject lines are more the result of their increased likelihood of being triggers than the length of the character count itself.

Worth noting, however, is that shorter subject lines also seemed to have above-average open rates even when limiting the analysis to triggered emails. This was true for Welcome emails, Reactivation emails, and Abandoned Cart emails, though longer subject lines had slightly higher open rates for Browse Abandon messages.

So it’s possible that the shorter subject line did have an impact independently of the email’s status as triggered or not. One aspect working in favor of shorter subject lines is the tendency to open emails on mobile devices, which generally display 50 or fewer characters, per Litmus research contained in the report. It stands to reason that the ability to read the entire subject line could help a recipient decide whether or not to open the email…

How does the Yes Lifecycle Marketing analysis fit with other research in this area? Here’s a quick look at the results of previous analyses:

  • There is no correlation between subject line length and read rate (Return Path, 2015);
  • Email newsletters with short subject lines of between 4-15 characters sport the best open rates (MailerMailer, 2014);
  • The longer the length (in characters) of a B2C email subject line, the higher its open rate (Adestra, 2012).

As you can see, there’s conflicting research, which makes it difficult to make broad generalizations about subject line length. But it’s at least instructive to add this study to the body of research.

What does seem clearer is that personalization can have a role to play: the fractional share (2.3%) of emails analyzed by YLM that were personalized had far higher open, click and click-to-open rates than those without personalization.

And the body of research concerning personalization seems a little clearer:

The full YLM report – based on an analysis of more than 7 billion emails sent during Q2 2017 through its platform – is available for download here.

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