How to write an email subject line people actually open

You write a good email subject line when you say in a few words what the recipient will find inside and why it is worth opening right now. Stay under 60 characters, put the most important part in the first 40, promise only what the email delivers and check the result with an A/B test. In this guide you will find eight proven ways to write an email subject line, with examples, four tips for fine-tuning it, and figures from research and from Quanda's own analyses that you can rely on.

In a nutshell

1. People look first at who the email is from. In Quanda's survey, the sender decides the open for 56 % of people, the subject line for 30 % and the preheader for 14 %.
2. In an analysis of 10,178 campaigns in Quanda, subject lines with 21 to 30 characters had the highest open rate. On mobile, often only the first 40 or so characters are visible.
3. There are eight proven approaches: a question, "How", controversy, a straightforward statement, money and big names, numbers, curiosity and urgency.
4. In a large experiment, the recipient's name in the subject line raised opens by 20 %. Only when it is correct.
5. The subject line must not promise more than the content. A disappointed recipient will not open the next email either.
6. Which subject line works for your audience you will only find out by testing. No general guide can tell you.

In brief: what a subject line should say, how long it should be, what does not work and how to test it

• What it should say: what the recipient will find in the email and what they get out of it. Specifically and truthfully.
• How long: no more than 9 words and 60 characters, with the key words in the first 40 characters. The preheader in Quanda up to 50 characters.
• What does not work: misleading promises, fake Re: and Fwd:, subject lines in all capital letters, a badly formatted salutation and a subject line more interesting than the whole email.
• How to test it: with an A/B testing campaign where the versions differ only in the subject line. Quanda picks the winner and sends it to the rest of the recipients by itself.

What has changed since publication: This guide was first written in 2019, and it now also includes the older article "4+1 ways to write an email subject line" from 2016, so you have everything in one place. I have added the results of our survey among email recipients, an analysis of subject line length across 10,178 campaigns sent through Quanda, research figures from 2023 to 2026, the recommended length, Gmail and Yahoo rules against deceptive subject lines, and the big change of the last two years: Apple, Gmail and Yahoo mailboxes have started summarising emails with artificial intelligence.

Your customers receive lots of emails every day. Many of them never get opened and go straight to the bin. The reason may be a dubious subject line that looks like spam, tries to sell something straight away, feels pushy, or is simply dull.

Your first job is therefore to write a subject line that stops the recipient from deleting your email the moment it arrives.

What an email subject line is and why it decides the open

An email subject line is the short text the recipient sees in the message list of their inbox before opening the email. Together with the sender name and the preheader, it makes the first impression on which a person decides within a few seconds whether to open the email, leave it for later or delete it.

According to the Consumer Email Tracker, produced by Validity for the UK Data & Marketing Association (DMA), the most common reason to open an email is that the recipient recognises the sender (61 %). The subject line comes a close second (57 %). If the subject line fails to catch attention, even the best content will not help, because nobody gets to it.

We asked the same question in our own survey: "What do you look at first when deciding whether to open an email?" The sender was the clear winner.

So the subject line comes second, but it is the part you can write differently, and better, for every campaign. You set the sender once, but you write the subject line anew every time.

Sources: the studies and recommendations listed, as of September 2026.

How to write an email subject line in 6 steps

This is the process I use myself, and it works for a newsletter, an offer or an event invitation alike. A good email subject line is realistic, short, personalized, relevant, original and informal, but not too informal. The individual steps keep an eye on these six qualities.

1. Start with the recipient. Write down in one sentence what they will find in the email and what they get out of it. The subject line has to answer the question "Is there something in here for me?"
2. Pick one of the proven approaches (a question, a how-to starting with "How", controversy, a straightforward statement, money and big names, numbers, curiosity, urgency) and write at least three versions of the subject line with it. I describe all eight approaches with examples in the section 8 proven ways to write an email subject line.
3. Move the most important words into the first 40 characters and cut the whole subject line to 60 characters at most, so it is not truncated on mobile.
4. Consider personalization. Insert a salutation only when the name data is clean and correctly formatted, and in a tone that matches your relationship with the recipient.
5. Write a preheader that complements the subject line rather than repeating it. In Quanda, it has a limit of 50 characters.
6. Check that the content of the email delivers what the subject line promises, and compare the two best versions of the subject line in an A/B testing campaign.

Tip: You do not have to start from scratch. Go through the subject lines of the emails you receive. Write down the ones that grabbed your attention instantly, the ones that stand out from the rest and the ones that made you open and read the email. You will quickly see which types work on you, and most likely on your customers too.

8 proven ways to write an email subject line

If you are not sure which type of subject line to choose, try them all and find out which works best. In the examples, replace "X" with a number and the words in brackets with something relevant to your business.

Ask a question

One of the best ways to get attention is to ask a question. Ask something that matters to the people you are writing to. People are curious and will want to find the answer to the question you asked. They open your email and look for the answer right there. If you use this type of subject line, always make sure the answer really is in your email.

Examples:

• "What is the fastest way to grow your company's revenue?" (for business owners)
• "How do you lose 5 kg in 5 weeks?" (for gym members)
• "How much does an email nobody opens cost you?"

Start with "How"

When you start your subject line with "How", you go straight for the curiosity of the people you are writing to. Who would not want to be more efficient, more successful, better looking, richer and so on? Just make sure the subject line is not the most interesting thing in everything you send. If you lure recipients in with guides, procedures or tips, make sure the rest of the content lives up to it. Take a self-critical look at the content of the email, and the landing page if there is one, and make sure you are giving people something of real value.

And if you disappoint them, they will not forget it. Remember going to the cinema because of a trailer you had seen a while back, only to realise at the end of the film that the trailer was the best part? A friend of mine recently signed up by email for guaranteed weight loss tips. It all looked great until the email arrived. In short, it said: "Eat less and move more." True, no doubt, but she expected something else. She unsubscribed and never wants to see another email from that company again.

Examples:

• "How to cut campaign prep down to half an hour"
• "How to simplify (task) without any new tools"

Use controversy

Use controversy, that is opposing views on topics you know your recipients care about. This approach again plays on human curiosity and the desire to get to the bottom of things. Who is right? What is the real story? Those are the questions people ask themselves when they read such a subject line, and they will want the answer.

Examples:

• "Why we no longer track email open rates"
• "(Popular advice in your industry)? Our data says the opposite"

Say what it is

Often the best approach is simply to say in the subject line what you want the recipient to learn. If the recipient knows you, a straightforward, simple subject line will often do the job. This works best when you know your readers' needs well.

Examples:

• "Friday night jazz at Ronnie Scott's: tickets now on sale" (for the club's fans)
• "5 ways to grow your company's revenue" (for business owners)
• "New templates for your spring campaigns are in the app"

Money and big names

If you manage to get money or a well-known big name into the subject line, you are well on the way to having your whole email read. Big sums, the names of famous people or large companies have always attracted attention, and they still do. The chance to earn money more easily, or not to lose it, is still a strong motivation to open your email and dive into its content. Only use a name, though, when it genuinely relates to the content of the email.

Examples:

• "How much (company) saved in its first year with (product)"
• "What (well-known expert in your field) told us about (topic)"

Use numbers in the subject line

This type of subject line remains popular and is used very often, and not only in emails. Take a look at magazine covers. They are packed with numbered headlines. Numbers are easy to remember and bring structure and clarity. Did you know that the most popular number is 10? A specific number also tells the reader how long the read will take.

Examples:

• "X mistakes that stop customers from opening your email"
• "3 changes in (field) coming your way in January"

Spark curiosity

Writing this type of subject line takes a bit of creativity. Done well, it instantly raises the curiosity of the people you are emailing. Do not forget to satisfy that curiosity and deliver information in a scope and quality that match such an attractive subject line. The content of the email must then correspond to the subject line for the whole thing to make sense.

Examples:

• "You won't believe your eyes" (a TV retailer with a new display)
• "Where it's all heading" (an email from one of our customers about trends in their field at home, in Europe, in the United States and in Japan)

Create urgency

If you manage to create a situation in which people feel the need to act, you have created what we call urgency. It can be real, or it can exist only in your wishes. When you tell people to do something right now, that is only your wish. But if you back that urgency up with a specific deadline and the chance to gain something, you create real urgency. This will not persuade someone who neither wants nor needs the thing to buy it. But those who want it or are considering it and are still hesitating will respond.

Examples:

• "Registration for (event) closes Thursday at 12:00"
• "Only 2 places left on (training course)"

Warning: The deadline must be real. Fake countdowns and a "last chance" that comes round every week are quickly seen through by recipients, who learn to skip your emails.

How long should an email subject line be

The ideal email subject line has no more than 9 words and 60 characters. That is Mailchimp's recommendation, which also suggests no more than three punctuation marks and one emoji at most. Klaviyo's 2025 data shows that the willingness to open an email drops as the number of words grows. The average subject line has around 7 words.

What Quanda's data shows

We looked at how subject line length relates to open rate across 10,178 email campaigns sent through Quanda.

Among the groups with enough campaigns, subject lines with 21 to 30 characters had the highest open rate, 18.9 %. Between 31 and 90 characters, the open rate stays between 15 and 16.6 %, and the lowest, 14.2 %, belongs to subject lines with 91 to 100 characters. Interestingly, subject lines with 11 to 20 characters also did worse (14.6 %). So a subject line that is short but says nothing does not help.

The practical takeaway is a simple rule: aim for around 30 characters. If you need more, that is fine, just put the essential part at the start. Length on its own matters less than what the subject line promises.

How many characters the recipient sees

How many characters the recipient actually sees depends on the device. Gmail in a browser shows roughly 70 characters, an iPhone in portrait only around 41. Since most people read their email on a phone, a simple rule applies: the essential part belongs in the first 40 characters. Treat the end of the subject line as a bonus for those who see it in full.

Sources: Omnisend, email subject line recommendations; Mailchimp, Best Practices for Email Subject Lines. Values vary by device, font and mailbox settings.

Tip: Always check the subject line in a test email on your phone before sending. You will see exactly what your recipients will see, including where the subject line gets cut off.

Personalizing the email subject line

The more the recipient feels you are talking directly to them, the more effective your communication will be. Whatever the style and type of subject line, the word "you" always helps: "The new swimwear collection, picked for you", "A car that suits you", "A suit tailored for you".

You can also extend your subject line with a salutation. When people receive an email with their name in the subject line, they almost always open it right away out of curiosity. One of the few rigorously measured experiments confirms this. Researchers Sahni, Wheeler and Chintagunta described a test on millions of emails in the journal Marketing Science: the recipient's name in the subject line raised the probability of an open by 20 %, sales leads by 31 % and cut unsubscribes by 17 %. According to Klaviyo, only 2.5 to 3.4 % of brands put the name in the subject line. So it is an opportunity most of your competitors are missing.

If you use personalization, avoid broken salutations. In English the name itself does not change form, so the risks are elsewhere: a missing value that leaves you with "Special offers just for you, !", a name in capitals such as "JOHN" copied from a form, or a full name where a first name should be. Clean up the name fields before you send and choose the surname with a title or the first name depending on who you are writing to. The salutation code is inserted in Quanda through Personalization in the text field, and then you simply copy it into the E-mail subject field above the editor. The procedure is described in the help article Personalization in campaigns.

Do not overdo personalization. If your recipients expect a formal tone and to be addressed by their surname, avoid familiarity and an overly chummy style. A travel agency for seniors will get nowhere with a subject line like: "Hey Mary, what's up? Fancy an epic trip at a crazy price?" And do not put the name in the subject line of every campaign. Now and then it is a nice touch, every time it feels mechanical. A few examples:

• "Mr Harris, sign up today. Only 2 places left."
• "Hurry, Emma, the 50% off sale ends tonight at midnight."
• "Ms Walker, short on time too? X ways to simplify (task)."

Do not forget the question "Is there something in here for me?"

When someone receives an email, the first thing they do is ask themselves: "Is there something in this email for me?", "What's in it for me?" At that moment they decide whether to open your email, leave it for later or delete it. So if the subject line contains nothing that convinces the recipient the email is worth opening and worth their precious time, the choice of what to do with it is clear.

That is why you should read the subject line through the recipient's eyes before sending. Not through the eyes of a company with news to share, but through the eyes of a person with forty other messages in their inbox. "News from our product range" says nothing. "Three new sizes you've been looking for" says what the recipient gets out of it.

No tricks or gimmicks

Write creative subject lines that help people get to the information you are sending, but not at any cost.

If you manipulate recipients into opening your email and they end up disappointed or annoyed by its content, you will have a harder time next time. And if you do it to them repeatedly, they will unsubscribe and you will lose the chance to stay in touch with them. Worse, they will mark the email as spam, and that damages delivery to everyone else.

Deceptive subject lines are now also explicitly forbidden by the mailbox providers themselves and by law:

• Gmail forbids subject lines starting with "Re:" or "Fwd:" in its sender guidelines unless the email really is a reply or a forward. The sender name must not be misleading or contain text that belongs in the subject line.
• Yahoo forbids deceptive subject lines and requires the spam complaint rate to stay below 0.3 %. Gmail watches the same threshold, as described in the article Gmail, Yahoo and Outlook requirements for bulk email senders.
• The EU E-commerce Directive 2000/31/EC requires in Article 6 that a commercial communication is clearly identifiable as such and that the person on whose behalf it is sent is clearly identifiable. EU member states apply it through their national laws.
• Recipients in the US are protected by the CAN-SPAM Act. According to the US Federal Trade Commission (FTC), the subject line must accurately reflect the content of the message.

Subject line, preheader and sender work together

The recipient never reads the subject line on its own. They see it next to the sender name and above the preheader. At Quanda we call this trio the magic three, and all three parts have to make sense together.

Sender. The sender is the name and address the email comes from. In our survey, 56 % of people look at it first, and according to the DMA and Validity survey it is also the most common reason to open. A specific person's name works much better than a bare address like info@. How to choose the sender:

• Do not use the email address alone, always set a sender name as well.
• Choose a name your recipients know. Your salesperson or consultant, for example.
• Pick a suitable format, such as "Lenka from Quanda", "Lenka Drobná | Quanda" or just "Lenka Drobná".
• It must be immediately clear from the sender who you are.
• Send from an address people would naturally reply to, not from noreply@ or info@.
• You can use different senders for different types of content and recipients.
• Use automatic sender selection based on the contact owner. Quanda then sets the salesperson responsible for the contact as the sender, as described in the help article Contact owner.

Preheader. The preheader is the short text that appears next to or below the subject line in the inbox. If you leave it empty, the email client takes the first lines of the email, often "View this email in your browser". The preheader should not repeat the subject line but complement it or complete its thought. In Quanda it has a limit of 50 characters so that it displays correctly in different email clients. It is covered in detail in the article 9 tips on how to create the right email title.

Content. The subject line, the preheader, the email and the landing page must tell one story. When the subject line promises a guide, the first paragraph of the email has to start delivering it.

How spam filters judge an email subject line

Lists of "banned words" have been circulating online for years, but their importance is overrated. According to Litmus, spam trigger words are largely a myth. Google says that Gmail's filters look mainly at the IP address, the domain, sender authentication and the reactions of users themselves. So what matters is who sends the email and how recipients react to their emails, rather than a single word in the subject line.

That does not mean the subject line does not matter. The spam test in Quanda, which you run on the Sending page, scores the email from 0 to 10 and lists two subject line issues among the most common content offences:

• A SUBJECT LINE WRITTEN ENTIRELY IN CAPITAL LETTERS,
• a subject line with unsuitable words such as sale, free or discount, especially combined with exclamation marks.

A subject line like that also looks loud to people, not just to filters. A recipient who thinks it looks like spam will mark it as spam, and every such complaint hurts the delivery of your next campaigns. How to run the spam test and read the result is described in the help article Setting up mailing in a simple campaign.

How AI in the inbox reads your email subject line

Since 2024, a new reader has been standing between your email and the recipient: artificial intelligence.

• Apple Mail since iOS 18.1 (October 2024) can show a summary of the email's content created by Apple Intelligence in the message list instead of its first lines, and it highlights priority messages. Since iOS 18.2 it sorts mail into the Primary, Transactions, Updates and Promotions categories. Summaries are shown for emails in English, so your recipients on iPhones with Apple Intelligence may see a summary before they see your content.
• Gmail made AI email summaries available to all users in January 2026, and since September 2025 it can sort the Promotions tab by relevance. Brands the recipient engages with most rise higher in it.
• Yahoo Mail has been showing one-line email summaries in its mobile app since November 2024.

What does this mean for the subject line? When AI summarises the content right under the subject line, a misleading subject line gives itself away before the recipient even opens the email. A subject line that accurately matches the content, on the other hand, is reinforced by the summary. Litmus points out this connection too. And since Gmail favours senders people actually engage with, it pays to write subject lines the recipient opens regularly, not one-off clickbait.

Tip: You can put artificial intelligence to work on your side too. Through the Quanda MCP server, your AI assistant, such as Claude or ChatGPT, looks at the aggregate figures of your sent campaigns, tells you which subject line features are linked to higher open rates for you, and suggests new subject lines on a given topic based on your own history.

A/B testing your email subject line

A/B testing is a type of automated email campaign that helps you fine-tune your subject line (and more). It lets you test your subject line in real time on real recipients.

How does it work? You create an email including its subject line. Let's call this version A. Then you copy the email to create version B. In version B you change only the subject line and leave the rest of the email identical to version A. You choose a test group of recipients and set how the winning version should be picked. In this case the winner is picked by open rate, since the subject line mainly affects this figure. Quanda takes care of the rest. It sends the test emails to two randomly selected groups of recipients, automatically evaluates the winning version once the time set for collecting statistics has passed, and sends it to the remaining recipients.

You can see in real time which subject line was more effective and find the words and word combinations that work best on your customers. It is an exciting game that you will not only enjoy but that will have a very positive effect on your email results. The full procedure is in the help article How to create and set up an e-mail campaign with A/B testing.

How long should the test run? Across almost 500,000 A/B tests, Mailchimp found that for tests decided by opens, two hours identify the long-term winner in more than 80 % of cases and twelve hours in more than 90 %. Quanda recommends setting 1 day, as results are most reliable after 24 hours.

What to keep in mind when evaluating: According to Litmus, Apple Mail accounts for 62 % of all opens, and many of them are made automatically by Mail Privacy Protection without the recipient's involvement. So take a small difference in open rate between versions A and B with a pinch of salt. Look at the click rate of the winner too. A subject line opened by people with genuine interest shows in the clicks.

Checklist before sending

Before you send a campaign, go through the subject line with this list:

• The subject line answers the question "Is there something in here for me?".
• The key message is in the first 40 characters, the whole subject line has 60 characters at most.
• The subject line does not promise more than the email delivers and is not the most interesting thing about the whole email.
• The salutation is correctly formatted and the tone matches your relationship with the recipient.
• The preheader complements the subject line, does not repeat it and fits into 50 characters.
• The sender is a specific person the recipient knows, with an address they can reply to.
• The subject line is not in all capital letters, has no row of exclamation marks and does not start with a fake Re: or Fwd:.
• Any deadline in the subject line is real.
• You have checked the test email on your phone.
• For an important campaign, you have two subject line versions ready for an A/B test.

Conclusion

Whichever approach you choose, it pays to spend time on a good subject line and test everything thoroughly. If your readers do not open the email you send them, they will never get the chance to see the information inside.

If you want to go deeper into writing emails, take the free online course Email Copywriting and Design That Gets Read. And if you are not sure how to approach subject lines in your industry, get in touch. We will go through your recent campaigns with you and tell you where you have room to improve.

Fingers crossed!