Q: Should You Capitalize Email Subject Lines? Or should they read like sentences?

Sometimes with the Stash we try to dig deep and uncover hidden ideas. But other times we just want answers to simple, common questions. For the next few weeks we’ll be doing just that around the theme of email subject lines. Today our thinking caps were donned for a common division between normal writing and subject line writing: Capitalizing the First Letter of Key Words. Does this writing style hurt or help open rates? Take a peek.

The Goods
To find an answer we looked at resort that used both the title style (i.e., “Capitalize the First Letter of Key Words”) versus the normal-sentence style (i.e., “Capitalize just the first word.”) in recent campaigns. Each campaign had been sent to at least 10,000 recipients to be included in the sample. Here’s how the open rates look when you compare these two approaches:

In this case there was a small difference between the two. When just the first letter of the subject line was capitalized, campaigns in our sample saw email open rates that were a half percentage point higher than their more title-like counterparts. Instead of about 16.2% open rates, they saw 16.7%.

What This Means
To be fair, the difference is rather small and could be attributed to other things. But when we tried to do a similar analysis for Twitter tweets we found almost no tweets that appeared like titles. This was almost exactly opposite of the numbers for email. In this regard, perhaps social is beginning to set the tone for other media.

This is one that we’d definitely split test if we were in your shoes. The next time you send a campaign, try turning your subject line into a normal looking sentence and see what happens. The difference may be negligible, but this analysis suggests it might be worth a try.