[Reply Research] How to Write Better Subject Lines, According to Data

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[Reply Research] How to Write Better Subject Lines, According to Data

Vlad Oleksiienko 26 May 2022

Effective cold outreach is a form of art… with a great deal of science thrown in!

If you’ve ever wondered why some emails drive results while others don’t, you’re not alone. Helping other sales teams ace outreach for the past 6 years, we at Reply have always wanted to crack the code and find a recipe for a perfect cold email.

That’s why we’re happy to announce the launch of Reply Research, a series of studies analyzing different aspects of cold outreach based on first-hand data from millions of emails sent using Reply.

So, let’s slip into our lab coats and dig deeper into the data, starting with the hidden patterns and actionable insights for effective cold email subject lines.

4 data-backed insights to help you write better subject lines

Just like every big brand has a catchy slogan, every successful cold email starts with a good subject line. It gives the recipients an idea of what’s inside that email while also triggering their interest to learn more.

Being the first thing someone sees when your email lands in their inbox, the subject line is also one of the main criteria they will consider before opening it.

To figure this out, our data scientists have analyzed 712K first-step emails with unique subject lines against these 4 key parameters:

Disclaimer: The average performance metrics for the analyzed emails that we will be using as the benchmarks in this research are 31.69% open rate and 3.02% reply rate.

If your emails already outperform these results, congrats! But the sky’s the limit, right? Why not try to do even better?

How to Write Better Subject Lines (According to Data)

How long should your subject line be?

One thing I’ve always been curious to find out is: Could the length of your subject line influence the open rates?

On one hand, many people check their inbox on their smartphones. So it totally makes sense to keep your subject lines short enough to be displayed in full on mobile (usually, 25-30 characters).

On the other hand, does this really have a direct effect on your open rate?

The answer is yes! According to our data, open and reply rates vary based on your subject line length.

What’s the takeaway here?

Always keep your subject lines short, ideally no more than 4 words, (but don’t leave it blank!) to get the highest open and reply rates.

Pro tip: If you’re looking for some inspiration, we have 4 subject line formulas (+ examples) ready to use.

Should you capitalize your subject lines?

As any other SDR Leader, I am not just sending outreach emails, but also receiving plenty of them from other salespeople. Recently, I’ve started noticing an interesting trend with many subject lines containing only lower case words, e.g., “ sales development consulting for reply.io” or “ reply.io lead generation services.”

Since it did catch my attention (and people seemed to be doing it on purpose), I got curious: Could the letter case used in your subject line really influence the open rate?

To find that out, we analyzed 3 variants of the same subject line containing:

  1. all lower case words → sales development process at reply.io
  2. most lower case words → Sales development process at Reply.io
  3. most upper case words → Sales Development process at Reply.io

Long story short, it could indeed influence the open rate, yet correlation isn’t that significant, according to the research:

As you can see, every little nuance can make a real difference when it comes to cold outreach.

So, if you’re looking to increase your open and reply rates, here’s a trick: Instead of coming up with the new subject lines, try capitalizing most words within the existing one and see what happens!

How many variables should you use in a subject line?

As you might know, I am really into personalization at scale. I myself got into experimenting with different types of variables in cold emails.

So, the next assumption I was eager to test was: Could adding more variables help me generate a higher open rate?

This time, we picked 4 subject line variants, based on the number of used variables, e.g.:

  1. 0 variables → your sales development process
  2. 1 variable → sales development process at {{Company}}
  3. 2 variables → {{FirstName}}, sales development process at {{Company}}
  4. 3 variables → {{FirstName}}, {{Company}}’s {{Year}} sales development

Here’s how the number of variables used in the subject line correlated with the average open rate.

Based on this data, we can assume that it’s generally OK to send cold emails with no personalized variables in the subject line as long as the messages are relevant.

If you’d like an extra touch of personalization (and a few more opens for your emails), go ahead and add two or more variables to your subject line!

Should you use emojis in the subject line?

Despite selling B2B, we always try to build and maintain friendly, informal relationships with our prospects. Yet, using emojis in cold outreach might seem too extreme. To clear up any doubt, let’s turn to the data.

So, our next question is: Could emojis really help your cold emails get more opens?

And without further ado, the answer is YES!

So I strongly encourage you to try this approach for some of your campaigns, or at least A/B test this subject line variant to make sure it works for your audience as well as it does for ours.

Cold email best practices to put the insights to good use

Based on the data insights listed above (plus some others that we will address next time), we’ve put together a short list with cold email subject line best practices. Feel free to steal it.

And remember: While a 30% open rate is ok, 50%+ is amazing! If your results are lower, your subject line is most likely to blame. Follow the tips listed above to fix it!