Beatriz Redondo Tejedor

// Head of Content

Ever wondered how to write the perfect email subject line? At Mailjet we ask ourselves that very question every time we put together our weekly newsletter for all you to read. Have we ever wished there was some sort of mythological magic, some kind of out-of-this-world secret weapon that would do all the hard work for us? You bet!

Well, let me tell you something. After a quest that’s made ‘The Twelve Labors of Hercules’ pale in comparison, we’ve finally found the Holy Grail. Yes, don’t look at me that way ?. We have. What’s our secret to killer subject lines, you’re wondering? Our A/X testing tool, of course.

You might be about to say: “Bah… I’ve been using a testing tool for quite a while now… Still not the answer I was looking for.

But… are you using it correctly?


lion king ab testing correctly


Finding the perfect email subject line with A/X testing

Finding the right subject line through testing requires a particular set of skills that not everyone is aware of. Namely, an ability to challenge your own preconception (cause, you know, you might not always be right), persistence and a commitment to regularly research new ideas.

A key component that many lack is the creativity or research skills to come up with new subject lines to test, tailored to the message they’re sending. In a recent talk at Figaro Digital’s Email and CRM Seminar, Dela Quist talked about the importance of testing a number of ideas, not just two (as traditional A/B testing tools do). Actually, his research found that the optimum amount is 10.


7 testing ideas to find the perfect email subject line

How many different things do you usually test in your email subject lines? Do you focus on your wording, your tone or the message itself? If you’ve answered one of the three, you’ll only be “partially correct”. The truth is you definitely need a combination of the three to ensure you find the perfect one for each campaign.



This is one of the most basic tests in some people’s eyes, but really something to look into. The subject line length allowed by different email clients and devices varies from around 70 characters on Gmail’s desktop version to just 30 characters on some of the smaller Android phones, so understanding this will help you pinpoint how long is too long.

But there’s another element to the length that a test will allow you to understand better. Do your readers feel intrigued by subject lines they can’t fully read? Or do they find this irritating and prefer shorter, more precise subject lines? Try a range and analyze the performance, both for each individual campaign, but also across different email clients and devices over a period of time.



Another basic one, but yet another one that can be easily overlooked. Does your audience react better when they see their name used in the subject line? We keep on talking about the importance of personalizing content to make it more relevant, but at the end of the day, your contact list is formed by a unique set of people with their own particularities. It could be that someone sends them a daily influx of messages with personalized subject lines, and they just instantly associate it with some unwanted marketing campaign that they automatically ignore.

personalized email subject line



To emoji or not to emoji? For today’s email marketer, that might actually be the question. The suitability of emojis will depend on your database’s age and location, their use of social media and even the device they read their emails on.


emojis email subject line


But it’s not just about whether to use emojis or not, but also which ones to use. Different cultures might react to the same picture in different ways and, no matter how many times they try to convince us, a peach is not always a peach. ? ?


Negative Statements, Questions & Exclamations:

The tone, the wording and how you phrase your subject lines will definitely have an impact on how your readers’ willingness to open your emails. You could be stating facts, sharing excitement or asking them a question to make them reflect on something. Maybe highlighting great things works best, or maybe your readers are more inclined to open emails that stress negative elements.

Would a salary comparison page get better results with the negative statement “You’re not being paid what you deserve”, the question “Are you being paid what you deserve?”, or an exclamation such as “We know how much you should be making!”? The only way to know is by testing.


FOMO / Clickbait:

Fear Of Missing Out is a thing. It is the psychological principle that rules Facebook: people want to know what other people know, what other people are talking about. Curiosity meets insanity, basically. So, are you leveraging your contacts’ FOMO with subject lines they just can’t resist?

To an extent, the basis of clickbait subject lines is precisely this overwhelming curiosity that pushes us to open a message to find out if, in fact, “there’s no way I can imagine what this person said”. Clickbait headings are all across the Internet nowadays and people are slowly catching on, but you’ll never know if they work with your audience unless you try them.


Vague / Straightforward:

You’ve probably heard about Obama’s email marketing success during his 2012 presidential campaign. Well, a big part of this was down to the interesting range of email subject lines his team picked, which caused impressive open rates and an all-time fundraising record. The team tested a huge number of subject lines, varying from straightforward messages such as “Thankful every day” or “Some scary numbers” to more vague ones, like “Change”, “I will be overspent” and even a friendly “Hey”.

vague email subject line


Discounts & Urgency:

Another interesting idea worth investigating if your company sends product emails is to see whether outlining discounts and promotions, or creating a sense of urgency on your subject line will generate higher open rates. Overusing time-limited campaigns and headings might become a bit like the tale of Peter and the Wolf, where your contacts stop trusting you and end up not reacting as you’d wish, because they know another offer will be coming their way soon. Be sure to test this frequently to find the right balance.

discount email subject line


There’s no limit to the things you can test. We’ve covered just a few of the possibilities here, but there are many more you can try. Want to find out if including the name of your brand in the subject line makes people recognize you more and be more willing to open your email? Try it. Think that including a profanity might generate some interest and spice up your contact’s dull inbox? Try that too! At the end of the day, finding the perfect subject line requires a bit of both art and science. ?


Have you been regularly testing your email subject lines? What have you discovered? Share your best performing headings and your most interesting examples with us on Twitter, using #EmailMarketing.