17+ Email Subject Line Best Practices to Boost Engagement

Illustration by Rodrigo Fortes Illustration of an email subject line in scrabble tiles

You can have the best email content in the world…but if you can’t engage subscribers with your subject line, all that content is going to go to waste. Instead of opening your emails, they’ll just keep on scrollin’ through their inboxes.

So – how can you write an email subject line that grabs your subscribers’ attention and encourages them to engage with the rest of your email?

Well, there are some tried-and-true email subject line best practices that you can implement, which is the subject of this post.

Below, you’re going to learn 17+ best practices that will help you write effective subject lines, while still retaining your unique voice and style.

These tips will help you generate genuine interest and engagement from your emails, which is essential in a post iOS 15 world where it’s harder than ever to track your subscribers’ actions.

Let’s get to it…

How to improve your email subject lines

Here are 17+ email subject line best practices, presented in no particular order. You might not apply every single tip to every subject line, but you’ll want to try and implement as many as possible for maximum results.

1. Write the subject line first

When you’re setting up an email, it’s easy to create the body content first and then come back to the subject line once you’re finished.

While some people can work effectively that way, it’s generally a better idea to start with your subject line first. That way, you can ensure that you’re not just throwing it in as an afterthought.

Writing the subject line also gives you a chance to directly connect the subject line text to the body text, which can make for more engaging emails in general if the body builds on the subject.

If you don’t want to totally commit before you’ve finalized the body of your email, you can try brainstorming a few variations to start, rather than choosing a final version. Then, you can pick the option that works best once you see how everything comes together.

2. Add some personalization

Instead of sending off the same generic subject line to every subscriber, try addressing each subscriber by their name in the subject line. Or, you can also experiment with other types of personalization, depending on the data that you have about each subscriber.

There’s data suggesting that people are anywhere from ~20-30% more likely to engage with personalized emails over generic ones.

Most email marketing tools make it easy to dynamically insert each subscriber’s name in your subject line. 

If you’re using MailPoet, you can check out our email personalization guide to learn how to set it up. All you need to do is include the relevant shortcode in your subject line. You can also specify a generic fallback in case you don’t have a certain subscriber’s name:

851.png" alt="Adding personalization to your email subject line

3. Ask a question?

Why do questions make for engaging email subject lines? Mainly because every question needs a good answer. So if the question in your subject line intrigues the reader, they’ll be more likely to engage with the email to get the answer.

Of course, the key here is that the question needs to be compelling enough to generate interest. You can’t just add a question mark to any sentence like you’re in Anchorman (I’m Ron Burgundy?).

For example, let’s say your email list is in the strength training space. Consider these two emails:

  • How to hit PRs every time
  • How can you hit PRs every time?

PR = personal record.

It’s essentially the same subject, but formulating it as a question makes it a little more engaging and can get you more clicks.

To take things further, you can go with the question and answer one-two punch, which is a pretty common strategy. Here’s an example:

How can you hit PRs every time? Try these 9 tips

4. Keep it short

Shorter subject lines are more effective than longer subject lines for a couple of reasons:

  1. A lot of people consume email on mobile devices nowadays, which means that there’s very limited screen space and longer subject lines will be cut off.
  2. People will often scan subject lines rather than reading them word for word, so a shorter subject line makes it easier to engage someone who’s quickly scanning.

Nowadays, we recommend keeping your subject lines under 50 characters. Additionally, try to put the most important words/details towards the beginning to account for people who are quickly scanning.

5. Create a curiosity gap

A “curiosity gap” is the gap between what we know and what we want to know.

If you can create a curiosity gap where people want to know what’s in your email, they’ll obviously be more likely to engage with your content.

A lot of clickbait titles are excellent examples of the curiosity gap. For example:

“X-Ray Scans of Ancient Egyptian Mummy Reveal a Surprising Discovery”

The curiosity gap is the difference between our existing knowledge of mummies and this “surprising discovery”. What is the discovery? We need to know!

If the headline provided all of the information right away, we wouldn’t feel as compelled to open the article because we already know the information (so there’s no curiosity gap).

Stop Clickbait has lots of other fun examples of clickbait, which is where we sourced this one.

Now, we’re certainly not saying you need to go full-bore into clickbait to create engaging subject lines. That will quickly lead to diminishing returns and risk turning off your subscribers as they get tired of your shenanigans.

But we are saying that there’s a reason clickbait headlines work, and it can be useful to understand that principle so that you can incorporate it into your own subject lines in a softer way.

6. Mix things up for recurring offers (like sales)

If you have a lot of sales, it’s easy for subscribers to become “blind” to your deals if you’re using the same subject lines over and over.

For example, imagine that you send “50%-Off Sale Today Only” every time you have a sale – customers might eventually tune that out because they’ve seen it before.

To fix this, make sure to mix it up when sending emails for sales and offers. It’s still important to include the 50% off in the subject line, but you can play around with the other words and target your deals towards specific events or conditions.

7. Be clear when clarity makes sense

Above, we told you that creating a curiosity gap can be an effective subject line to drive engagement with your emails.

However, there are also times when it’s better to be clear and upfront.

This is the tough part of writing effective subject lines – there are no hard rules that apply to every single email. You need to adapt your strategies to your audience, as well as the content and purpose of your emails.

Let’s say you’re about to launch an awesome 75% off sale. You could try to create a curiosity gap by writing something like “Something big just dropped…”.

But in this case, it’s probably just better to lead with the 75% off sale detail because that’s already pretty engaging by itself! There’s no need to try to get overly creative – just let your awesome deal do the talking.

If you’re sending multiple emails, though, you can try mixing things up. For example, if you’re teasing the 75% off sale a week in advance, you might go with something mysterious like “There’s something big brewing…”.

But when it comes time to actually launch the deal, you want to hit them with that 75% off number in the subject line so that people know exactly what’s happening.

8. Add identity words

Identify words are words that connect with the self-identities of your subscribers. This can be especially powerful if you have a niche audience who you know are all focused on certain topics.

For example, let’s say your website is about helping freelancers grow their businesses. In this situation, you can be pretty confident that most of your subscribers will self-identify as freelancers (or at least want to get to a place where they can become a freelancer).

Instead of writing a subject like this:

How to work more productively

Try adding identity works like this:

How freelancers can work more productively

By including the identity of the reader, you build a connection and make your email more engaging to that person.

9. Include numbers (and use numerals)

Including numbers in your subject lines is a great way to boost engagement.

For example, Campaign Monitor A/B tested these two different headlines:

  1. 3 steps to measuring the success of your email marketing with Google Analytics
  2. How to measure the success of your email marketing with Google Analytics

They found that the first subject line (with the number) had a massive 57% higher open rate than the second headline.

Both high and low numbers can be effective, but in different situations:

  • High numbers are effective when you’re providing value to the subscriber. For example, “17 tips for improving your subject lines” – more tips = more value so a higher number is better. The same is true for sales/discounts where a higher discount means cheaper prices.
  • Low numbers are effective when you’re talking about the effort a subscriber needs to take. For example, “2 steps to a faster-loading WordPress website”. The lower the number of steps a person needs to take, the less effort they’ll need to expend. Less effort is good, which is why a low number is more effective here.

Finally, you always want to use the actual numeral instead of writing out the number. That is, “3 steps to…” is better than “Three steps to…”

10. Add some urgency or scarcity

Urgency and scarcity are tried-and-tested marketing tactics for driving engagement and interactions. You might also see this called fear of missing out, AKA FOMO.

If people feel like they might miss out on something, they’ll be more likely to take action to avoid having to feel FOMO.

For example, if you’re promoting your freelance business coaching services, you could try something like:

Only 3 freelance elevation coaching packages remain

Only if it’s the truth, of course. Using false scarcity isn’t cool, and might even run afoul of the law in some jurisdictions.

If you’re promoting a sale, you could use something like:

Our Sale Ends in 6 Hours

Adding those elements of urgency encourages people to click on your email right now rather than scrolling by (and maybe never coming back to your email).

11. Harness social proof

Social proof is a great marketing strategy across all of your digital platforms, including your email subject lines.

The basic idea is this – “other people think we’re great, so you’ll probably think we’re great, too”.

You can go with raw numbers – e.g. “lots of people think we’re great”. Or, you could highlight specific influencers – e.g. “George Clooney thinks we’re great”.

You can also play around with combining social proof with other strategies on this post, such as a curiosity gap.

For example, if we’re sticking with our freelancer coaching example, you could try something like “423 freelancers found a client using this strategy”. There’s social proof from the success of people using this strategy, and there’s a curiosity gap because people want to know what this successful strategy is.

12. Play around with emojis 😂

Ok, there’s some debate with this one, which is why it’s “play around with emojis” instead of “you absolutely should use emojis in your subject lines because they always work.”

With that being said, a lot of brands have had success with incorporating emojis into their subject lines, especially if the brand has more of a playful brand personality.

There’s data showing that including certain emojis in your subject lines leads to higher engagement…but there’s also data showing that other emojis can lead to lower engagement than the alternatives.

If you want to learn the best practices here, check out our guide to using emojis in email subject lines.

13. Pay attention to sentence case and title case

One common question for optimizing subject lines is what capitalization you should use.

There are two viable options:

  • Title case – How to Write Good Subject Lines
  • Sentence case – How to write good subject lines


Both are ok to use and you’ll see both used quite frequently.

In general, using sentence case feels a little more personal, which can make it a good option when you’re trying to build a connection with readers.

On the other hand, using title case feels a bit more formal, which can make it a good option for business-focused emails or transactional emails.

We recommend playing around with both approaches to see which works better for your specific audience.

14. Use your FROM name and email

When people open their email inboxes, pretty much all email clients will show at least two pieces of information for each email:

  1. Your subject line, which is what we’ve been focusing on in this entire post.
  2. Your FROM name, which typically appears to the left of the subject line.

If there’s more space, some email clients will also show the preview text, which is our next tip.

This makes your FROM name another valuable piece of real estate for driving engagement with your emails.

You’ll want to choose something straightforward that people will instantly associate with your brand. Typically, your brand name itself is a good starting point.

Some people also like to use real names to create a more personal connection. However, using just a name alone can be confusing because people have no way to associate the name with a brand. If you still want to try it, consider a hybrid approach like “Colin at MailPoet”.

And no matter what, don’t use “noreply” as your FROM name if you want people to engage with your emails.

15. Connect the subject line to the preview text

Ok, this one isn’t exclusively about the subject line. But some email clients will display both the subject line and the preview text next to one another.

This means that you can tie them together to further boost your engagement.

For example, if you formulate your subject line as a question, you can use your preview text to tease users with the answer to that question.

If you’re using MailPoet, you’ll get a separate field to enter a custom preview text. This field appears right below the subject line:

Email subject line best practices for preview text

16. Learn from other brands

One of the best ways to improve your subject lines is to be a little more mindful when you’re scrolling your own inbox.

Pay attention to which email subject lines make you the most likely to engage. Then, try to apply those lessons to your own subject lines.

If you don’t want to go scrolling in your own inbox, you can also check out our collection of the best email subject line examples to get some inspiration.

17. Avoid these pitfalls that negate your results

So far, we’ve talked about a lot of positive things that you can do to improve your email subject lines.

However, this post wouldn’t be complete without discussing some of the biggest email subject no-nos that could reduce the effectiveness of all your hard work.

Here’s a quick rundown of what you should not do in your subject line:

  • Use spammy words/phrases – certain words or phrases have been abused by spammers and as such can hurt your subject lines. HubSpot maintains a pretty detailed list of spam trigger words and phrases to give you an idea of what can cause problems.
  • WRITE IN ALL CAPITALS – this is pretty clearly annoying, right? Most users think so too. And if that’s not enough, using all capitals increases the chance of hitting the spam folder. In very rare situations, it might make sense to capitalize a single word. But you need to REALLY be careful if you’re doing that.
  • Overuse exclamation marks!!!!! – one exclamation mark in a subject line is ok. But adding a bunch can look spammy (and is more likely to actually trigger spam filters).
  • Don’t use a question mark and an exclamation – “Are you getting flagged for spam? Stop using exclamations after questions!”. This format naturally looks a bit spammy, which is why it can be an issue in your subject lines.

For more things to avoid, check out our post with 11 signs that you might accidentally be an email spammer.

Implement these email subject line best practices today

If you want to create more engagement with your emails, focusing on your subject lines is key.

Your body content could be the best in the world, but you won’t generate clicks unless your subject lines do a good job of grabbing your subscribers’ attention.

In this post, we’ve shared 17 different tips to help you write better subject lines and drive more engagement from your email efforts.

Try them out today and see how they work for you.

If you’re using MailPoet, you’ll be able to easily track the engagement for each email subject line so that you can find the formulas that work best for your specific audience.

If you’re not using MailPoet yet, sign up today for free to start getting more from your email marketing efforts.

Do you still have any questions about these email subject line best practices or getting the most from your email subject lines? Let us know in the comments!