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Posted by Matt Osborn - 28 June, 2019

4 Tips to Help You Write Effective Email Subject Lines

35% of email recipients open email based on the subject line alone.

Do you pay enough attention to composing the subject lines for your marketing emails?

At Omnisend we often receive various questions from our clients on how to improve this or that.

Sometimes we get the questions that we don’t know the answers to. When that happens, we look at our data from all our marketers and often we find the answers there.

This time it was the research on the subject lines.

We tried to find the answers to the most often questions about the subject lines asked by our clients. I do believe that our insight can come in handy to more email marketers.

So here we go.

1. Does personalization in the subject line have any effect on open rates?

By saying personalization, I mean adding the first recipient’s name in the subject line. 

I have found random articles on the internet that say - personalization would improve the open rate.

So we wondered whether personalized subject lines would really make people open it more or not

The data showed that personalized subject lines aren’t so popular among marketers. Only 3.5% of emails sent had the recipient’s name included.

When comparing the personalized subject lines with not personalized ones, we see that using the recipient’s name in the subject line increases the open rate only 0.2%.

18.1% personalization open rate beats 17.9% non-personalized open rate. This small difference isn’t even statistically significant. 

So the answer to the previous question is: personalization has no real effect on open rates.


2. How do exclamation marks effect open rates?

Whereas the bulk email campaigns have different open rates from automated email workflows, we broke our analyzed data down into these two categories.

It allowed us to provide more accurate numbers.

Bulk email campaigns

The data showed that 42% of all newsletters sent had subject lines with exclamation marks, and 58% had none.

The subject lines without exclamation marks had an 18% open rate. Meanwhile, the subject lines with exclamation marks had a 17% open rate - a full percentage point lower open rate on average.

When digging deeper, it came to the daylight that the more exclamation marks had been used, the lower open rates were. See the chart below. 


Automated email workflows

The data was surprising: 95% of all automated emails that Omnisend clients send contain exclamation marks. 

When sending a series of automated emails, subject lines with 1 exclamation mark performed better again - the open rate of 24%. 2 and more exclamation marks had a negative effect on open rates. Those emails only had a 21% open rate. 

When sending a single automated email, the results were respective: a 47% open rate vs. a 42% open rate. 

Therefore, don’t shout at your recipients in the subject lines. Stick with no more than one exclamation mark per subject line. 2+ exclamation marks will bring down your open rates.


3. Which discount works better: percentage or dollar amount?

The interesting fact is that 10 times more marketers used the % sign in their subject lines, in comparison to the $ sign, but the $ sign fares better in terms of open rates.

The average open rate with the % sign was 25%. Meanwhile, the $ sign had an open rate of 29%.

Here the psychology plays the main role. We can only guess that the $ sign worked better because the email recipients perceived the offer as of higher value.

Or maybe the dollar amount didn’t require them to do any math - they get what they see.

Before including the discount into your next subject line, ask yourself: which discount SOUNDS like a better deal? 

For example, if you sell accessories for mobile phones for $20. A 25% discount, I guess, would work better than a coupon for $5.

However, if you’re really concerned about which discount will bring the best result, do the A/B test before rolling out the campaign to all your audience.


4. How long should your email subject lines be? 

From our analyzes, we learned that the most subject lines have between 11 and 50 characters on average. The average open rate of emails with this length of subject lines was 33.8%. 

The subject lines with 11-50 characters are good for practical reasons as well: both - desktop and mobile - users can see the entire subject line. 

Now take a look at the chart below.


What is interesting, there also were a few longer subject lines (with 51-90 characters).

They got a 40.5% average open rate.

But we should take into account that the sample was much smaller than the one with shorter subject lines. So to claim that longer subject lines work better wouldn’t be statistically accurate. 

So looking at the data in the chart, I would say that subject lines between 21-30 characters have the best open rate, and these subject lines also happen to be the most popular.


Usually, the marketers spend hours on designing a perfect email campaign and the subject line emerges only in the last steps before launching the entire campaign.

However, don’t underestimate this small line. The success of your campaign ultimately depends on it.


How to make an effective email subject line

  1. Personalization makes little difference

  2. Do not use more than 1 exclamation mark

  3. Use currency symbols over percentages

  4. Only use 21-30 characters

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Topics: B2B eCommerce, B2B Sales, Sales & Marketing, B2B Marketing