The Trouble with Email Subject Line “Best Practices”

Email Subject Line

Too often marketers become frustrated trying to come up with subject lines that will communicate their offer so compellingly that subscribers just can’t help but open the email. No wonder then that there are thousands of articles out there offering advice for crafting the perfect subject line. But how many of these articles provide insights that are new to seasoned marketers and give you a real edge over the competition?

Subject line length doesn’t matter, but don’t go crazy – Mailchimp

Mailchimp looked at data from 12 billion email sends and concluded that subject line length does not correlate with opens. Yet in their own Best Practices for Email Subject Lines guide, Mailchimp recommends keeping subject line length to 50 characters or fewer. This doesn’t necessarily contradict their research though.

Certain words, such as compound words for product names, are simply longer than others. If you need to use such words, your subject line will necessarily be longer than it would be otherwise. Still, a pithy line is probably better than a verbose line if you have a choice. This brings us to the next point.

Getting the wording just right

There is no shortage of articles out there that advocate using language in certain ways to entice readers into opening your email. Copyblogger, a respected source for writing tips, recommends that subject lines be:

Useful: Is the promised message valuable to the reader?
Ultra-specific: Does the reader know what’s being promised?
Unique: Is the promised message compelling and remarkable?
Urgent: Does the reader feel the need to read now?

These are solid guidelines. Getting to the point quickly at the right time is crucial. Yet there is more to a subject line than wording. Being useful and ultra-specific, for example, necessarily involves aligning your message with the appropriate audience. And here we get into the territory of segmentation and targeting.

Traditional segmentation and targeting

Sending offers to people who want those offers rather than people who have no interest in said offers will help improve open rates, CTRs and purchase rates. We completely agree with those who advocate and practise segmentation. It sounds obvious because it is, which is all the more reason you should employ such tactics rather than shoot in the dark. But what if you could shine a light into those dark spots?

The ability to segment beyond intuitive and obvious categories like gender, age or even past-purchasing behaviour within pre-existing product categories confers tremendous value. This is the sort of work Coherent Path does for our clients.

What we’ve found from our own data: open rates and subject lines don’t matter much (if your goal is to generate revenue)

If your goal is to get an email read then open rates certainly do matter. But if your goal is to generate revenue, metrics like purchase rates clearly matter more. If you have stellar open rates but a poor purchase rate, the emails aren’t doing their job.

After working with a client of ours using our Campaign Optimization solution to optimize for cross-sells into high value but previously unpopular categories, we found that subject lines had little impact on the efficacy of an email in terms of generating revenue. We also found that open rates weren’t the strongest predictor of an email’s ability to generate revenue.

This is seen in the difference between a control group and the test group upon which our solution was used. While the test group only had a 5.61% lead over the control group in open rates, it produced a click product rate that was 27.78% higher and increased the purchase rate by 37.5%, resulting in $1,211,148 more in revenue.

The key to this success wasn’t better subject lines – in many cases the subject lines were exactly the same – but rather identifying new and counterintuitive product categories for cross-sells and matching these with receptive segments. Our software was able to do this by mapping out each individual customer’s journey and identifying which products intersected with these journeys at various points in time. It also determined how customers could be gently nudged towards product categories that were new to them, but which they would nevertheless like. You can read more about that here.


Don’t agonize over subject lines and don’t read too much into open rates. Instead focus on determining what your subscribers like and sending them emails that reflect this. To achieve major improvements though, you must go beyond conventional segmentation. Customer journey-informed segmentation enables you to induce cross-sells, increase revenue and improve lifetime value. New technology, such as that offered by Coherent Path, allows you to do this automatically.

Download: A Closer Look at the Science Behind Coherent Path