The Ultimate Email Subject Line… You’ll Never Believe It!

by | Email Marketing

The Ultimate Email Subject Line… You’ll Never Believe It!

by | Sep 23, 2015

We’re channeling our inner Buzzfeed today.

Hyperbole aside, we were actually quite surprised when we learned this, and, well… Almost didn’t believe it until we fact-checked for ourselves

The ultimate email subject line for open rates is…

…no subject at all.


What’s a subject line?

An email subject is your first opportunity to win – or lose – a prospect’s attention. It is the most important and, sadly, most neglected part of any email you’re sending. Any email.

We did the fact-checking for you.

The following is based on the analysis of over 30 million emails sent from outlook and gmail. We didn’t do the counting, but we did check the maths.

Top 5 Best Subject Lines

  1. “RE:”
    92% Open Rate
  2. “RE: Follow Up”
    90% Open Rate
  3. “RE: Update”
    89% Open Rate
  4. “RE: Introduction”
    88% Open Rate
  5. “RE: Checking In”
    87% Open Rate

Top 5 Worst Subject Lines

  1. “The Results Are In”
    7.25% Open Rate
  2. “4 Management Headaches that Can Be Solved in One Hour”
    8.35% Open Rate
  3. “10 Secrets for Driving Accountability and Accelerating Business Results”
    8.39% Open Rate
  4. “Are Your Students Protected”
    9.36% Open Rate
  5. “10 Secrets for Accelerating Business Results”
    10.92% Open Rate

What can we learn from this?

Well, first there is a clear difference in the length of the top performing and worst performing subject lines. Subject lines with more than three words have an average open rate of 15%  or lower.

The second most obvious difference is the topic of the subject lines. The top performing subject lines are personal, and by using “RE:”create the impression that the receiver has already been involved in this conversation. If we look at the worst performing subject lines, 3 of the 5 are clearly Buzzfeed style post updates, and imply that what lies within is automated and generic – the opposite of the “RE:” effect.*

There are other factors at play here. For one, iOS is now responsible for a staggering 35% of all email first** opens. Forgetting Android even exists, more than a third of emails are opened on an iOS device. There isn’t much room for long subject lines to be displayed on a phone in portrait mode.

*I’m going to coin that term.**People will open your email on their phone and, if it’s important, go back to it on a desktop.


  • Take advantage of the RE: Effect™.
    Using “RE:” by itself is hugely effective, and is also associated with high open rates of two to three word subject lines.
  • Keep it SHORT.
    Long subject lines are dramatically out performed by three words or less.
  • Use your new powers for good.
    Use these tips sparingly. Your list will quickly become immune to your magical subject lines, and if your emails are irrelevant or uninteresting, they’ll stop opening them. Use these tips for when it really matters – when you’re delivering a sales pitch.


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