Subject Lines Live – Best of April 2021

Since the beginning of April, we have been gathering the highest-performing email subject lines from across the Spotler universe; that is, all of our own sends and everything our customers have sent using the platform. You can check out the daily top 5 here.

As befits the email nerds that we are, we decided to investigate the full set of data for patterns and insights that we could share, to inspire you in your own quest for better email performance.

April’s Overall Top 5

Rank Subject Line CTR (%)
1 Our mission to provide incredible service 86.71
2 [sender] Software Update 85.99
3 Product Catalogue 2021 80.35
4 Here is your [sender] design guide. Let’s get started! 75.43
5 Download your Make a Difference in a Day resources! 74.76


1: “Our mission to provide incredible service”

The top dog for the whole month took our team by surprise. At first glance, it’s a banal platitude, without any supporting statistics or social proof.

However, focussing on service as a differentiator, rather than anything that your product does, is a smart move. Add that to the moral power of the term “mission”, and you can start to see why nearly 87% of recipients engaged with this subject line.


2: “[sender] Software Update”

This subject line’s strong performance is more predictable. When you rely heavily on a software tool, any update that affects how it works is worthy of your attention.

Additionally, in an inbox crammed with flowery wording and bright emojis, a straightforward subject line stands out. With simplicity and clarity, you know exactly what you’re getting. A possible takeaway from this finding is that adding an event invite or other CTA to the bottom of your functional sends is likely to be an effective tactic. We are NOT recommending that you use this kind of subject line to disguise a blatantly sales-y email!


3: “Product Catalogue 2021”

While this is a little more sales-oriented than #2, much of the same logic applies.

When Anthony Stears, The Telephone Assassin, spoke at GatorCon2020, he emphasised that cold calling is a lot like your local takeaway dropping a menu through your letterbox. They aren’t going for an immediate sale, they’re making sure they’re in your mind next time you don’t feel like cooking. This approach is the same; “Here’s what we offer, drop us a line when you need something.”


4:Here is your [sender] design guide. Let’s get started!”

We’re big fans of sending resource downloads in an email; it earns you a place in the inbox, and it’s another opportunity to put your brand in front of the reader.

This subject line takes it to another level by adding a push to take action. How often do you download a resource, only to let it sit for a week? Or worse still, you forget all about it.


5:Download your Make a Difference in a Day resources!”

You put a lot of effort into crafting resources to offer value to your leads and support your sales team. But if you just put them on your website and don’t tell anybody about them, you will never get the full benefit.

By describing what the resource is, this subject line is more compelling. “Have you seen our new brochure?” is in the same vein, but bland and lacking urgency.


What about the rest?


The most common bracket for April was 51 to 60 characters. In English (the language that the vast majority of our customers use), the average word is 4.7 characters long. Therefore the average subject line length is 10-12 words.

None of the highest performers had fewer than 11 characters. This is unsurprising, as it’s hard to say anything meaningful in such a short amount of text.

At the other end of the scale, nearly 10% stretched over the 100-character mark. It seems that if you are going to go with a long subject line, there is no point using half measures!

Oddly, there was an empty gap between 80 and 100 characters. If your subject lines are this long, it’s quite likely they are “fluffy”; using lots of words that don’t make your point or add extra value.



67 of 75 top subject lines, 89.33%, did not include any personalization. For the purpose of this analysis, “personalisation” means using dynamic text to insert the recipient’s name into the subject line. In GatorMail it is also possible to insert the recipient’s company name, but none of our top performers chose to do this (e.g. “How #[CompanyName]# could do better marketing with GatorMail”).

For more on exactly what personalisation means in the context of subject lines, check out That Phrasee Episode of That Marketing Podcast.



Only 5% of April’s high performers included an emoji.

The most likely reason for this is that emojis can display differently across different email clients, and so it is tricky to create a uniform experience, or even to be sure they will show up at all in some cases!


Sender Name

As the average office worker’s inbox now receives an average of 120 emails per day, a simple way to jog your reader’s memory of who you are is to include your company name in the subject line, as 2 of April’s top 5 did.

However, this is not a common option among the rest of the pack, with slightly fewer than 1 in 6 using this tactic. Instead, it is more effective to have a regularly recurring sender name for your comms, as people connect better with people than with faceless brands.

Now over to you!

There are many ways to judge the effectiveness of a subject line, and plenty of ways to cut the data. However, if nothing else, we hope this has encouraged you to think about the subject lines you use, and even the ones you receive, with an analytical eye.

The best thing you can do with a data set like this is to use it as a springboard for your own experiments. Our regular Great British Split Test is underway for 2021; you can read the results of the previous one here.

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