I recently analyzed 60,000 subject lines to answer questions like, “Is shorter is better?” You know — just for fun.

I learned some interesting things that might challenge your assumptions about subject lines.

First, subject length could matter, or, it could not — but mostly, not. You may see research to the contrary, as in this recent Buffer article. But I question the approach used in some of this research. To put it simply, comparing your view rate to my view rate is inaccurate since we have different lists, different audience demographics, different frequencies, and different subscription practices. Not to mention different email topics!

How I Analyzed Subject Lines

Instead of analyzing all 60,000 subject lines to see which ones performed best, I looked at a batch of 60,000 subject lines but only compared them to other subject lines from the same sender. In other words, I looked at the subject lines that gave individual senders’ view rates a lift over their average view rates. Specifically, I focused on emails that had at least 5 percentage points more views than average for that sender.

Thus, if someone consistently had view rates between 10% and 13%, I looked for her one email that got 18% or higher. If another sender generally had a view rate between 45% and 50%, I looked for a view rate of 55% or more before analyzing the subject line itself.

What I Learned About Subject Lines

  • Shorter subject lines often drive more views — IF the sender’s subject lines are typically very long. In the example below, the email with the shortest subject line got more views than the average email from this sender (10 percentage points more views). Note that content definitely plays a role as well. “Sad News” is undoubtedly compelling.

example of a shorter subject line performing well

  • Personal-sounding subject lines often get above-average view rates. In the example below, “A Warm Farewell” got more views than the average email from this sender (15 percentage points more views). The content of this subject line is also intriguing — we’re not sure who is leaving.

example of a personal-sounding subject line

  • Some RSS to Email senders who use the exact same subject line every week see fluctuations of 10% in their view rates. Huh? (Clearly, it’s not just about subject lines.)

The Bottom Line

  1. Always share the most genuine content you can in your subject lines. Don’t oversell, and don’t clickbait it. Just let people know your content is valuable.
  2. When appropriate, make your subject lines personal. I don’t mean that you need to include someone’s name. But subject lines that read like you have a personal relationship with your customers, or have news about you (and not your business), tend to lead to high view rates.
  3. Use the “Compare” tool on Mad Mimi’s dashboard to get a big-picture sense of how your subject lines are performing. For example, select your 5-10 most recent emails, click “Compare,” and look at the “Viewed” tab. Do any of your emails stand out?
  4. If you find yourself slipping into a ho-hum subject line pattern, surprise your readers by shaking things up a bit!