Email Subject Lines – 5 Steps to Improve Open Rates

email marketing

Creating a perfectly crafted email without thinking of an engaging, enticing subject line is the same as painting a masterpiece and hiding it behind a brick wall. Essentially, all of your efforts are wasted.

Follow our email marketing guide to learn how to draft subject lines that ensure your emails get opened and that your hard work does not go to waste.

How important are email subject lines?

If you imagine your emails are a party, your subject lines are the invite. They are the window into your business’s latest promotional communication; an electronic, text-only billboard that encourages people to see what you have to say.

Did you know… 124.5 billion business emails are sent and received each day?

Study conducted by Radicati.

The average inbox is now more crowded than ever before, and in order to compete with the latest ASOS or John Lewis email marketing message, you need to stand out. The sole aim of your subject line is to encourage the recipient to open your email. Neglecting to put the time and effort into creating an engaging subject line is like expecting to be let into a building without ringing the doorbell or knocking on the door.

Getting sick of the metaphors? Sorry, how about a fact instead?

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


A common error in email marketing is leaving the subject line to the last minute, rushing it as a necessary bit of admin as opposed to a crucial part of your marketing.

Yes, the body of your email is what drives people to your website or to your store, but the only way people get that far is with a subject line that stands out from the many other promotional e-shots that make their way into their inboxes.

What impact do open rates have on my email marketing?

An open rate is the percentage of people that open your email in comparison to the number of people who receive it. Open rates are calculated by dividing the size of your email list by the number of unique opens.

Why are open rates important? Because the more a user opens your emails, the higher your future communications will rank in their inbox. Email providers such as Gmail and Outlook are becoming increasingly intelligent, able to determine and prioritise certain emails over others to make the whole process of checking your emails even more efficient and seamless for users.

Hoping to improve your open rates? Check out MailChimp’s Guide.

email subject line

1. How long should an email subject line be?

It’s important to bear in mind that many people now use a mobile device for the majority of their email communications. Such devices usually have slimmer screens, meaning less room for a lengthy subject line.

As a general rule of thumb, a punchy subject line using five words or less will evoke the best open rates.

Two thirds of emails are now read on mobile devices.

According to Marketing Land.

The above stat not only underlines the importance of a mobile-friendly design in the body of your email. It also makes the length of your subject line absolutely crucial. It’s all very well having a clever subject line, but if it cuts off half-way through on mobile, you’ll no doubt lose a lot of potential openers (and most likely, therefore, customers).

Using MailChimp, Campaign Monitor or any other email marketing provider’s analytics, you should be able to tell what devices people are using to open your emails. If the majority of your opens stem from mobile devices, we would recommend a subject line using no more than 40 characters. Any subject lines within this bracket should display on most Android, Windows and Apple devices.

If you know that almost all of your recipients open your e-shots via desktop, you can get away with being a bit less succinct, with anywhere between 50-70 characters. For a more detailed overview of character limits on email clients and devices, check out Campaign Monitor’s Guide below:

2. How to avoid spam filters with email subject lines

The spam folder is where marketing emails are sent to die. Sorry if that sounds a little dramatic, but it’s true! If your email ends up in a Spam folder, it means the email client (think Gmail, Outlook, Yahoo Mail) has flagged your communication as dodgy and potentially dangerous to the recipient.

Only 79% of emails sent by marketers reach the recipient’s inbox.


When creating a subject line, there are certain words and phrases that are big no-no’s if you want to swerve the dreaded spam folder. Here are a few of them:

  1. Hundreds/thousands/million/billion/trillion etc.
  2. Free/discount/no obligation/best price/cash/money.
  3. Multiple exclamation marks.
  4. Guaranteed/easy/extra/risk free.
  5. Billing/income/debt.
  6. 100%
  7. Click here
  8. Cures
  9. Urgent.

Your ‘From’ address and name also play an important role in spam filters. Make sure you are sending from an authoritative email address and that your From name appears trustworthy and on-brand. In the mean time, check out SimplyCast’s list for more words likely to trigger spam filters.

69% of people mark emails as spam based on their subject lines.

email subject lines

3. What tone should I use for my email subject lines?

The best subject lines stand out from the crowd and engage the user enough to encourage them to click. Your tone will of course depend on your brand’s voice and what works in your other marketing communications, but when writing a subject line, think about what entices you to open an email.

There are many ways you can increase opens with your subject line: using humour to entertain the reader into wanting more; writing something to ignite the recipient’s curiosity; an offer that creates urgency; or a question that engages the user into providing or discovering an answer.

The easiest way to land on a successful tone for your subject lines is to send the exact same email with different subject lines, then analyse the data and optimise the next email accordingly. This is called A/B testing. If one subject line generates more opens than another, you have a valuable insight into how to write the next one.

4. Should I use emojis in my email subject line? 📧👍 or👎

We are seeing an increasing number of brands use emojis in their email subject lines, but are they effective?

Emojis certainly have their advantages: they add a bit of colour and imagery to help your email stand out from the those with plain-text subject lines, and can also serve to save space. On mobile, you have about 30-40 characters before your subject line is cut off. If you can convey a lengthy word or phrase in a singular character/emoji, it’s definitely worth doing so, as long as it fits in with your branding and target market, of course.

If you seek an emotional response to your email’s subject line – something that can certainly help with open rates – emojis are an excellent way to do this.

While there are multiple benefits to including emojis in your subject line, you need to remember that these do not render on all devices. Older versions of Outlook, for instance, will display your lovely little heart or smiling face as the word “emoji”, instead. Not ideal…

A great way to know for sure whether emojis resonate with your recipients is through A/B testing.

5. Personalising an email subject line

Personalisation in marketing can be fantastic in building trust and adding value between consumer and brand, but does it have a place in email subjects?

By adding a recipient’s name to an e-shot’s subject, you are making an immediate connection with the recipient, showing them that you know who they are, giving them the confidence they have invested in your company in the past, whether that’s through signing up to your email database or purchasing something from your shop, for instance.

Personalised subject lines generate 26% more opens.

Campaign Monitor

Additional knowledge of your customers that you can use to your advantage include:

  • Birthdays – Offering a one-off voucher to someone on their birthday is a brilliant way of building brand loyalty.
  • Anniversaries – Do you know when they last bought from you? Is it about approaching the time they need to renew or repurchase?
  • Location – Comply with location-specific trends such as weather and events.

Make the most of our email marketing experts

Need help turning your subscribers into paying customers or clients? Hoping to boost the number of leads you’re driving to your email subscriber list? Looking for guidance on how to create the ideal landing page?

Whatever you need, our creative, results-driven team of experts are on-hand to help. Get in touch now to learn about our range of digital marketing services. We’d love to work with you!

Oliver Wilkinson
Content Manager