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What makes a subject line work? Episode 4: Phreshness

Email subject line performance can be impacted by many, many things.


It’s just one of the many, many reasons the team here at Phrasee find subject lines so fascinating.

An email subject line’s relative quality can (and often does) mean the difference between a successful email marketing campaign that generates revenue, and one that falls flat and generates… nothing.

Here at Phrasee, we’ve been experimenting with email subject lines for years with the help of our awesome AI technology. We’ve found that there are a few key factors in how an email subject line is constructed that directly impact that subject line’s performance.

They are:

We’ve decided to share what we’ve learned about these key subject line elements with our email marketing compatriots over four blog posts.

This week, we look at subject line freshness. Or, as we like to call it: “Phreshness”…


What is “Phreshness”?

When you hear the word “Fresh”, what comes to mind?

If you’re like us, it could be this:

Image credit: NBC


But if you’re not, it’s probably something more like this:

Image credit: Studio Canal


When it comes to email subject lines, both are important.

Like the Fresh Prince of Bel-Aire, a phresh email subject line should stand out from the others in its neighbourhood (the inbox), but that’s a blog post topic for another day.

***Note: our AI can help you with that, too!***

When we talk about subject line phreshness, what we’re really referring to is that subject line’s linguistic uniqueness when compared to the subject lines a brand has sent before.

Linguistic variance – using drastically different words and phrases for different email subject lines – is what phreshness is all about.


Why does it matter?

If you send an email marketing campaign with a particular email subject line, and that campaign performs exceedingly well, you might logically assume that attaching a similar subject line to your next campaign would be the wisest course of action.

TIP: You might very well be wrong!

In actual practice, sending email subject lines that are linguistically similar (ie. Using the same words and phrases) will invariably produce diminishing returns with each subsequent send, regardless of how amazing the original subject line was.

Here at Phrasee, we call this phenomenon “Subject line effectiveness decay”. And trust us, it’s really a thing. Or, don’t trust us. You are welcome to test it out learn the truth for yourself, like we did!

The truth is, sending email subject lines with higher degrees of linguistic variance consistently results in higher performing email marketing campaigns.

And if that’s not a good enough reason to keep things phresh, we don’t know what is.


How can brands put this information into use?

Making a concerted effort to inject more linguistic variance into your email subject lines is an excellent step that any brand can take towards better email subject line performance.

Every brand (and every audience) is different. Trying out new types of language in regular split tests, with a solid plan in place to learn from the results of those tests, can help you identify which kinds of language and linguistic variance your audience responds to.

Always keep in mind that the words and phrases your brand uses in its email subject lines will reflect (for better or for worse) on your brand and its unique tone of voice. Every touchpoint is a branded moment, and protecting consumer perceptions of your brand should always take precedence.

Luckily, with enough testing data to draw from, striking the right balance between high performing subject line phreshness and your unique brand voice is entirely possible – as long as you are willing to invest the time and effort necessary to find the right balance for your brand.

If you keep testing, and keep subject line phreshness front of mind when building your brand’s email subject lines, you’ll soon see your email marketing ROI grow.

Look, the bottom line is this: There are a million things that make a subject line work. So many in fact, that we couldn’t possibly break them all down for you. If you REALLY want your email subject lines to do more for you and your brand, AI is the tool that can help you get there.

Book a demo with Phrasee to find out how!

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Trevor Beers, Senior Language Technician, Phrasee

Phrasee pheatures: Trevor Beers

Our very own Senior Language Technician, Trevor Beers, shares advice for those looking to join the tech industry, and insights into life at Phrasee.

Discover how applying actual AI to language can deliver big results!