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Subject lines: 5 things every email marketer should know

When designing an email marketing campaign, what subject line to use is often the last thing brands think about.


Which is weird, because it is the first thing the campaign’s recipients will see.

Constructing a top-notch email subject line is a subtle art, and one fraught with peril.

There are so many things every email marketer should consider when writing a subject line, no blog post can cover them all.

But, for a start, here’s 5…

Subject lines: 5 things every email marketer should know

1) Length is irrelevant

subject lines: 5 things every email marketer should know

Many blog posts cite statistics that claim to prove there is an “optimal” email subject line length. But, many of these statistics have been generated using faulty methodologies and are therefore unreliable.

We here at Phrasee studied the relationship between marketing email subject lines and open rates in depth, and drew a different conclusion:

The length of an email subject line has almost no effect whatsoever on open rates for marketing emails.

While this may seem counter-intuitive, it is nonetheless a scientific, mathematical, statistical fact. We’d like to point out that we came to this conclusion by analysing open rates from hundreds of thousands of marketing emails.

When writing an email subject line, email marketers now have one less thing to obsess over!

2) Sentiments are more important than words

In marketing language, the words we choose matter.

But not as much as the underlying sentiment does!

Words in a subject line are interdependent. One affects the other (and vice versa). Anyone who tells you an individual word in a subject line is better than another hasn’t done their homework – and doesn’t understand subject line science!

Analysing the sentiment of a subject line is much more useful than analysing the individual words used (this tool is quite helpful).

Understanding this simple subject line fact can help in two ways:

Both of these are extremely important for any email marketing campaign.

3) Split testing matters

If there was a person out there somewhere in the world who could accurately predict which email subject lines would drive the most opens, clicks, and revenue, that person would be very wealthy indeed!

Luckily, we haven’t met that person yet (because if they did exist they’d put us out of business in a hot minute!).

But at least we have split testing!

Split testing marketing email subject lines to determine which delivers the best results can have a massive impact on the open rates of any campaign.

Yet, oddly, many email marketers still don’t bother to do it.

But they should. They really really should.

4) Everything is always changing. Always.

If we’ve said it once, we’ve said it a thousand times: what works today might not work tomorrow.

The same principle holds true for email marketing in general and email subject lines in particular.

Maybe you struck gold a time or two with a well crafted subject line. Maybe those subject lines outperformed your previous ones by a wide margin.

Does that mean that duplicating that successful subject line, or changing a word or two, will produce similar results for your next campaign?


It’s the law of diminishing marketing language returns.

It’s like in the late 90’s when rapper “2Pac” represented the pinnacle of hip-hop fame in the years leading up to his untimely death. In due time, 2Pac found himself posthumously replaced by his apparent successor “3Pac”.

How’d that go?

See for yourself:

5) There are billions of ways to say anything

subject lines: 5 things every email marketer should know

Finding the best way to say something is a subtle art.

Punctuation, sentiments, calls-to-action, nouns, verbs, adjectives… language is complex.

Constructing a subject line for your marketing email that is on-brand, expresses your desired sentiment, and (most importantly) drives opens, conversions and ROI is no simple task.

Keeping this fact in mind when writing the subject lines for your next campaign can make all the difference in the world.

A good subject will get eyeballs on your email, while a bad subject line will do just the opposite.

And isn’t eyeballs what this is really all about?

6) ***BONUS*** Getting a little help can make a BIG difference

Subject lines: 5 things every email marketer should know

When it comes to email subject lines, no person or company has the wealth of knowledge and experience we at Phrasee do.

When you couple this experience and knowledge with the best AI technology in the email marketing game, you’ve got a recipe for subject line success!

If you want to find out more about how Phrasee can make your next email marketing campaign more effective, book your demo now!

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