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Does punctuation in a subject line help or hurt email performance?

Has the smartphone made the period as a punctuation mark obsolete for text messaging? Where the full stop once marked the end of a sentence, the simple line break has assumed that role in texting. The stop itself has evolved into a shorthand symbol that charges an otherwise innocuous sentence with deeper meaning, such as sadness or anger. It’s less obvious than emoji and takes fewer taps on the keyboard.

What does a change in text messaging behavior have to do with email? The demise of the period in text messages raises some interesting questions about email subject lines with stops at the end. Do they help or hurt opens, clicks and deliverability? And what about other punctuation marks? Do question marks drive more traffic? What about exclamation marks?

To get some answers, we turned to Subject Line Pro’s universe of virtual subscribers to see what impact punctuation marks had on their propensity to engage with subject lines containing punctuation marks. Subject Line Pro’s algorithm has the results of over 2 million subject lines from which to learn, so we were confident that our virtual tests would produce real insights.

Here’s what Subject Line Pro’s virtual subscribers told us:

The Full Stop or Period

The stop is an elusive mark. Marketers are split evenly into three camps: Some believe every subject line should end neatly with a stop; others believe that subject lines are best ended with no punctuation at all; and the rest can’t be bothered to care about a stop.

The data, on the other hand, is more definitive. It shows that stops do have a real effect on open and click rates. Moreover, the best results are achieved when stops are used sparingly. If you use stops intermittently in your subject lines (2% to 4% of your subject lines), they tend to take your subscribers by surprise (“Wait, what? A stop!”). Thus, they’re more likely to pay attention. This translates to a boost of 10% to 20% in open rates.

Ending with a stop also has a positive effect on delivery rate. The increase in engagement that comes with a stop results in a 0.5% increase in deliverability.

On the other hand, if you’re overzealous with the use of this punctuation mark, the data suggests you’ll see a drop of 5% to 10% in open rates.

Bottom Line on Periods:

2% to 4% of your subject lines should end with a single stop. Those subject lines will drive a 10% to20% higher open rate.

The Question Mark

The question mark is frequently over sold. “Create a sense of mystery,” the experts say. It makes the subscribers curious about your email and makes them more likely to open.

The virtual subscribers disagree. Using question marks had dramatic negative effects on click rates across the board, despite having no noticeable effect on delivery rate or on open rate. In fact, 72% of brands see a lower click rate – 8.1% lower on average – on subject lines that end with a question mark compared to other subject lines.

Although these types of subject lines are indeed good at generating attention, they perform poorly at triggering the right kind of opens: those from people with genuine intent to buy your product. While these two effects cancel out when it comes to your open rate, your click and conversion rates will suffer, as will your revenue.

Of the three punctuation marks we studied, only the question mark generated sharply negative click results. It’s not the question mark itself; rather, it’s how you use it. You’re probably asking questions that are too generic and failing to answer them in your email copy. You might get more opens than usual but fewer clicks.

The key to asking a question in the subject line is to have it be specifically about what the copy/products/offer is about. Doing so enables the question subject line to set and then fulfill expectations. High opens and low clicks usually mean you’ve set an expectation but failed to meet it in the email message.

Bottom Line on Question Marks:

Most clients see an 8% decline in click rates on the subject lines that end with a question mark.

The Exclamation Mark

Can exclamation marks really convey excitement to the bored recipient of an email? Doubtful, but that’s not the point. Contrary to what many believe, the objective of the exclamation mark is not to get recipients jumping up and down upon reading about your sale. Rather, it should be used as a marker that denotes a particular sale is special.

By using an exclamation mark, you are saying, “There’s a great deal here and it is so good we wanted to make sure you didn’t miss it by adding an exclamation mark.”

The good news: this works! When looking at brands that use the exclamation mark sparingly, we find that more than 70% of them see a lift in their open rate when they use it – and that lift is usually about 10% to 20%.

Bottom Line on Exclamation Marks:

Exclamation marks work and should be used as part of your subject line strategy. If you don’t over do it, you could expect to find subject lines that end in exclamation marks generate an open rate 1% to 20% higher than your average.

The Take-away

Overall, it’s clear that the winning strategy is one where you mix things up. Changing punctuation often is a great way to catch your subscribers’ attention and keep them engaged in what you have to say. Even something as innocuous as adding a single stop at the end of your subject line can be enough.

Keep in mind that our results were based on running tests against our entire virtual database. Your results may vary, so it is important to test these findings against a replica of your own database. Fortunately, that’s something that is easy to do with Subject Line Pro.