Making Sense of Subject Line Research

A very interesting study of subject lines was released last week by our friends at Alchemy Worx. The headlines focus mostly on length – is longer better than shorter? Is 40 characters better than 50 or 70? Let the debate rage, but I recommend ignoring it.

Focus instead on the key question this study helps answer: Whether subject lines of any length can predictably impact response rates.

Most of us think that subject lines only impact open rates – if the subject line is compelling, then the message breaks through. This is certainly true, but the Alchemy Worx report rightly also focused on broader engagement.

According to the study, open rates are optimized when the subject line is shorter – probably because shorter subject lines focus on a very specific offer. For example, “10% Off Until Thursday” is short, and compelling and easy for the subscriber to immediately understand the offer. If that message resonates, the subscriber opens. Certainly all the research we do here at Return Path supports this – clarity and simplicity in a subject line is always better than cleverness or complexity.

What I found more compelling is that the study focuses on click to open rates – which can be a much better measure of subscriber engagement for most marketers. A shorter subject line did not deliver as high a click to open rate – thus the higher volume of opens did not translate to a higher number of clicks. Here, the longer subject lines did better, although the click to open rate is higher not because there more clicks, but because there were fewer opens. So engagement was higher, but off a smaller pool.

Why? Alchemy Worx poses a few theories in the report, but what makes the most sense to me is recognizing that the subject line does not operate in a vacuum. Subscribers use the subject line IN COMBINATION with the actual message or the preview pane. If the subject line is simple, it piques the interest of more subscribers, but that raises the bar for marketers to close the deal (and drive a click and conversion).

In a postal mail analogy, the subject line is the envelope – it engages recipients to open the package. But if the content of the newsletter or promotion does not fully engage, then the open is wasted (unless you count a branding benefit). The subject lines must be linked closely to the offer, and the content has to follow up completely on the promise of the subject line.

Is that too obvious? That email marketing is still marketing – and direct marketing at that? Obvious or not, I feel that many marketers miss this opportunity (look at your own inbox for validation!) . Looking for magic bullets like the optimal length or the best day of the week can not replace the important work of making sure that subject lines and calls to action are completely aligned. We always recommend that marketers write the subject line at the same time they write the copy, headline and call to action. That way, the elements are working together to the same benefit: engaging the subscriber.

I also suggest that every marketer mimic the Alchemy Worx methodology on your own file – take a look at all the mailings you’ve done over the past quarter or year, and measure opens, clicks and click to open rate by length of subject line. In which direction does your own history guide you? Do keep in mind that it may not be solely due to length – if shorter subject lines are promotions and longer are newsletters, then your engagement rates will be completely different. Be careful to evaluate your program in a balanced method.

What I love about this approach is that it’s a much better measure of actual subscriber engagement and behavior than A/B split testing. Let me know how your file performs or if you would like help setting up the analysis.

minute read

Popular stories



BriteVerify email verification ensures that an email address actually exists in real-time


The #1 global data quality tool used by thousands of Salesforce admins


Insights and deliverability guidance from the only all-in-one email marketing solution

GridBuddy Cloud

Transform how you interact with your data through the versatility of grids.

Return Path

World-class deliverability applications to optimize email marketing programs

Trust Assessments

A revolutionary new solution for assessing Salesforce data quality


Validity for Email

Increase inbox placement and maximize subscriber reach with clean and actionable data

Validity for Data Management

Simplify data management with solutions that improve data quality and increase CRM adoption

Validity for Sales Productivity

Give your sales team back hours per day with tools designed to increase productivity and mitigate pipeline risks in real-time