How to Craft the Perfect E-Mail Subject Line

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This fall we walked you through the 5 steps of optimizing email performance. In the blog, we cited a study by Mailshake, which explained that e-mail subject lines are the single most important consideration a recipient mulls when deciding whether to open an email.

As someone who writes multiple email campaigns every week, I must admit that even I sometimes fail to invest the proper amount of time thinking about the e-mail subject lines. Those 40-some-odd characters are just easy to gloss over. I’ve been working harder lately to avoid this fatal flaw.

Imagine a salesperson without an opening line. It doesn’t matter how good the rest of his pitch is; he’s probably already blown the sale. Here are some tips to boost your subject line performance.


The average consumer receives dozens of emails per day. When that many voices are competing for your attention, a natural sort of filtration process kicks in. Breakthrough that barrier by communicating a clear value proposition in the subject line. And to be clear, “value” doesn’t need to relate to money; it can also relate to education or exclusivity.


Last week I received the following subject line: “The savings account banks don’t want you to see.” I am not in the market for a new savings account, but the subject line was so compelling that I couldn’t help but click. Indeed, curiosity is a powerful weapon. Consumers are seduced by cliffhangers and subject lines are ripe with opportunity to exploit this. A word of caution, though: make sure the actual email content pays off the provocative subject line, so your recipients don’t feel like they were misled.


Much like the content that lies inside, shorter subject lines typically perform better. According to Constant Contact, the sweet spot is 40 characters, which uncoincidentally is the length at which most mobile email clients truncate subject lines. Instapage points out that subject lines with exactly 5 words generate a 15.9% increase in open rates over longer ones. If your subject line needs to be longer, at least structure it so the most important information is frontloaded.


If you’re not testing your subject lines, you’re doing it wrong. At the end of the day, we can make reasoned calculations, but we can’t predict with certainty whether a subject line will perform up to par. That’s where testing comes in handy. Create at least two subject lines and test them against each other. You can do this by isolating 10 to 20 percent of your email list and sending Version A to half of that population and Version B to the other half.

By Alex Altman

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