Email Subject Line Research 2018: Short is the Latest Trend

MD M Nauman Thursday, 25 October 2018 0 comments
We’ve taken a comprehensive look at all emails and associated data sent last year to gain new insights into the importance of subject lines. The aim of this is to learn more about how to get emails open, read, and converting. By taking all of the data available we’ve been able to draw up a list of key questions that we intend to answer in this article.

1. Does Personalization Improve Open Rates?

In this instance, personalization refers to adding the person’s first name to the subject line. There is always the option to add the full name, but this can often appear too formal and is not appropriate.

The key thing to understand is that whilst personalized subject lines may seem like a nice touch, do they actually improve the open rate?

Personally, I feel that personalized subject lines run the risk of appearing spammy. As a recipient, I know that I am receiving an automated email, which makes the use of my first name feel insincere and not genuine.

Interestingly, when we began to crunch the numbers we found that only 3.5% of emails sent actually employed a personalized subject line. We then saw that the open rate for emails using a personalized subject line was 18.1%, as compared to the open rate of 17.9% for non-personalized emails. This is not a statistically significant difference as a larger sample could see the difference reversed.

It is clear that the data shows personalization has no demonstrated impact on open rates.


2. Do Exclamation Marks Add Emphasis, Or Reduce Conversions?

After compiling the top 30 performing subject lines used with newsletters we noticed that 14 of them contained exclamation marks.

By looking at newsletter campaigns and automated email workflows we were able to investigate whether their inclusion had any impact on conversion rates.

A. Newsletter Campaigns
42% of email subject lines contained exclamation marks, so how did this translate into conversions?

Subject lines that didn’t use exclamation marks had an open rate of 18%, as compared to 17% for subject lines using exclamation marks.
Interestingly there was also a negative correlation between open rates and the number of exclamation marks. With one exclamation mark, the open rate was 17.5%, falling to 16.7% for 2 exclamation marks, and16.5% for 3 exclamation marks or more. A clear sign from the data that users are put off by the use of exclamation marks.

B. Automation Workflows:

We found that a total of 95% of all automated emails sent by Omnisend marketers used exclamation marks.

Interestingly a single exclamation mark leads to an open rate of 29%, whilst multiple exclamation marks caused the open rate to increase to 35%. 

It’s important to understand that the sample size for multiple exclamation marks was far smaller and was therefore far more susceptible to being easily biased. 

There are also take-home points to be learned from looking at single emails and sequences of emails separately. 

Single Automated Email: Emails with a single exclamation mark achieved a 47% open rate. This then fell steeply to 42% when multiple exclamation marks were used.

It’s important to understand that the multiple exclamation samples were only 0.7% of the total sample size. 

Automated Email Series: The use of a single exclamation mark resulted in an open rate of 24%,  2 or more saw a drop to 21%.

This tells us that if you’re creating an email sequence then you will see a drop off in open rates when using multiple exclamation points. There are a number of possible reasons for this, such as reduced confidence that the message isn't spammed, but the numbers don’t lie. 

3. Should You Offer Discounts in Dollar Amounts or as Percentages?

At Omnisend we’re regularly asked about the best way to offer a discount. Should it be as a dollar amount (save $15) or as a percentage (get 15% off)? 

To gain some fresh insight into this problem we looked at subject lines containing a $ sign and compared them with those containing a % sign. Here’s what we found.


Interestingly the % sign was 10 times as popular amongst the marketers we looked at, but this didn’t translate into better performance. The dollar sign was underutilized and yet it leads to a higher open rate.

The open rate for $ sign subject lines was 29%, which was 4 percentage points higher than the 25% achieved by % sign subject lines. Proof that it pays to tell people the absolute amount of money they will be saving, rather than focusing their attention on margins.  

4. What is the Length of the Ideal Subject Line?

Interestingly we found that one of the biggest brands in our survey had a tendency to use very long subject lines.

We found that most subject lines used on average 11-50 characters, but why? Is this the most effective length? Or does the brand using over 200 characters on a regular basis know something that everyone else has missed?

Take a look at the graph below which charts open rates and include a curve showing which are the most commonly sent subject line lengths. 

Email Subject Lines Trend 2018

Interestingly you see that longer is better, to an extent. Subject lines with 51-90 characters show a 40.5% open rate, whilst the more commonly sent 11-50 character subject lines achieve a much lower open rate of 33.8%.

It is again important to take into account sample size and the ease of biasing. The red curve clearly shows that the size of the sample for the 51-90 character subject lines is significantly smaller and therefore more likely to be skewed. 

To get specific, it is seen that subject lines with 21-30 characters achieve the highest open rates. 

Indicating that short is the latest trend there is probably no need to regularly send long subject lines if you want to maximize the open rate of your emails. 

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