This guide is about writing email subject lines a reader will actually open. It covers what to put in the line, what to cut, and how to test one line against another. The subject line is the only part everybody sees, so it decides whether anyone reads the rest.
Writing a good one is not a trick you learn once. Strong email subject lines come from knowing who is reading, what you are really offering, and how the line will look on a phone at seven in the morning.
What email subject lines are really competing with
Your email does not arrive on a blank page. It arrives in a list, wedged between a delivery notice, a bank alert and eleven other senders.
The reader is scanning that list rather than reading it. A scan gives each line a glance, not a study. So three things carry the decision: the sender name, the subject itself, and the preview text that trails after it.
So the job is smaller than most people think. A subject line does not have to sell anything. It has to make the next second obvious.
The sender name does half the work
Before anyone reads a word of the subject, they read the name beside it. A name somebody recognises turns a cold line into a familiar one.
Keep that name steady. If a business sends as "Marketing", then "Newsletter", then a person's name, it has thrown away the one signal that needs no explaining.
Because recognition counts for this much, a plain line from a trusted sender usually beats a clever line from a stranger. Fix the sender name first when it keeps moving around.
Writing email subject lines a reader can decode in a second
Say what is inside. That sounds obvious, yet most weak lines fail exactly here, because they describe a feeling instead of the contents.
Specific beats clever
"Your order is on the way" tells somebody something. "Big news from the team" tells them nothing, and it costs the same to send.
Clever lines work when the reader already likes you. For everyone else plain wins, since a joke they have to decode is a joke they will skip.
Front load the words that matter
A phone shows the first few words and cuts the rest. So put the point at the front rather than the wind up.
"Friday: the workshop is full" survives that cut. "We wanted to let you know that the workshop has now filled up" does not.
Weak email subject lines and stronger ones, side by side
The difference is rarely about wit. It is about whether the line names something real, as these pairs show.
| Weak line | Stronger line | What changed |
|---|---|---|
| Our January newsletter | Three things that changed for landlords in January | Names the contents rather than the container |
| Do not miss out | The workshop closes on Thursday | A real deadline, so the urgency is true |
| Quick question | Quick question about your quote | Honest, because it says what the question is about |
| Hello there | Your size is back in stock | Relevance instead of a greeting |
Preview text is the second half of the line
Most inboxes show a short snippet after the subject. Leave it empty and the inbox fills the space itself. Usually it takes whatever comes first in your template, often a line about viewing the email in a browser. So the space goes to waste.
Treat the two together as one thought with a break in the middle. The subject makes the promise, then the preview adds the detail that makes it worth a tap.
Write it by hand for every send. It takes a minute, and it is the cheapest improvement available in email.
Email subject lines that quietly cost you trust
Some lines lift opens today and cost you far more later. They are worth naming, because they are common and they all work the same way. Each one borrows attention the email cannot repay.
- Fake replies, such as "RE:" on a message nobody ever sent.
- False urgency about a deadline that never actually passes.
- Anything promising news the email does not contain.
- Shouting in capitals, which reads as noise rather than emphasis.
- A first name dropped in only to prove that you have it.
Every one of these teaches the reader to distrust the sender name, which is the asset you spent months building. Worse, readers who feel misled reach for the spam button instead of the unsubscribe link. That choice follows you into every future send. Reaching the inbox at all is a separate discipline, and our piece on deliverability covers it, but misleading lines are one of the quickest ways to lose that ground.
Personalisation, and where it stops working
A first name in the subject is not personalisation. It is a mail merge, and readers worked that out years ago.
Relevance is what actually works. A line naming the item somebody left in their basket means far more than their name ever will.
That depends on knowing who is on the list and why, which is the job of segmentation rather than of clever writing. Once you split the list sensibly, the lines get easier to write, since each one only has to speak to one group.
How to test email subject lines without fooling yourself
Most tools offer a split test on the subject, and most people run it badly. Three habits fix that.
Change one thing at a time. Two lines that differ in length, tone and offer teach you nothing, because you cannot tell which difference moved the result.
Give the test enough people to mean something. On a small list a handful of extra opens is noise, so treat the outcome as a hint rather than a finding.
Then judge the winner on what happened after the open. A line can win the open and lose the click, which usually means it promised more than the email delivered. Since open rates now carry noise that nobody can strip out, the honest scoreboard is clicks and replies.
A worked example, with round numbers picked to make the arithmetic easy rather than to show a typical result. Send version A to two hundred people and version B to two hundred people. A gets forty opens and eight clicks. B gets fifty opens and six clicks. On opens alone, B looks like the winner. Yet A brought more people to the page, so A is the line to keep.
Length, emoji and the rest of the fiddly bits
There is no correct length, only a correct opening. Shorter lines survive a phone screen better, although a longer line that reads naturally still beats a short one that reads like a slogan.
Emoji are neither magic nor poison. One can add a flash of colour in a crowded list, while four in a row make a business look careless.
Avoid the old formatting tricks: brackets stuffed with labels, capital letters used for emphasis, rows of exclamation marks. They date quickly, and readers stop noticing them faster than marketers stop typing them.
Keeping a record of the email subject lines that worked
Every send teaches you something small, and almost nobody writes it down.
Keep one simple sheet: the line, the date, who received it, and what happened after the open. After a few months you own something better than any list of formulas, namely evidence about your own audience.
Patterns turn up quickly. Perhaps your readers respond to dates and ignore adjectives, or they open anything that names a town they know. No general advice can tell you that, since it is true of your list and nobody else's.
Where email subject lines fit in the wider programme
A subject line cannot rescue an email nobody wants. When opens fall across every send, the cause is usually the offer, the list or the frequency, not the wording of one line.
If that is the pattern, the fix sits upstream of the wording. Our guide to what email marketing is covers the parts a subject line leans on, namely the list, the offer and the timing.
The place email subject lines matter most is the welcome series. That is when a new reader decides whether your name is worth opening again, and the first two lines set that expectation for everything after.
Frequently asked questions
How long should an email subject line be?
Long enough to be clear, and front loaded so the cut does not matter. Every inbox truncates at a different point. The same line can survive on a laptop and lose its ending on a phone. So write the line, send it to yourself, and look at it in the app most of your readers use. If the opening words do not stand on their own, rewrite the front rather than trimming the tail.
Do emoji in a subject line help or hurt?
Test it rather than trust a rule. An emoji is a picture the device draws, so it can look different from one phone to another. Occasionally it does not draw at all. Send yourself a preview on a phone and on a laptop before a big send. Then check the line still reads properly without the emoji, since it should decorate the meaning rather than carry it.
Should I put the reader's first name in the subject?
Usually not, because readers recognise a mail merge instantly and it no longer signals any effort. Relevance beats a name every time. A line that mentions the item somebody looked at, the branch they visited or the date of their appointment shows real knowledge of them. If the only personal thing you can add is a first name, the line is better off without it.
How do I test email subject lines on a small list?
Carefully, and with lower expectations. A split test on a small list gives you a difference too small to trust, so treat the outcome as a hint rather than a decision. Run the same comparison across several sends and look for a pattern instead. Testing email subject lines properly needs one changed variable at a time, enough people for the numbers to settle, and a rule agreed in advance about what would count as a winner.
Why did a subject line that worked once stop working?
Because novelty was part of why it worked. A format the reader has not seen before earns a second look, and by the fourth outing it is just another line from you. Tiredness also comes from frequency, so a list that hears from you daily wears out any pattern faster. Rotate the shape of your lines, and keep the ones that describe real contents rather than the ones that lean on a trick.
Can a subject line send my email to the spam folder?
Indirectly, yes. No single word sends mail to spam by itself, which is the myth worth dropping. What really happens is that a misleading line makes people mark the message as spam. Complaints are one of the signals a provider weighs when it decides where to put your next message. So an honest line protects your delivery, while a line that overpromises damages it for every send that follows.
What should the preview text say?
It should continue the subject instead of repeating it. Most inboxes show a short snippet after the subject line, and if you leave it empty the reader sees a stray line from your template. Use it for the detail the subject had no room for, such as the date, the location or the name of the person writing. Write it by hand for every send, since it only takes a minute.
Are open rates a fair way to judge email subject lines?
Only partly, and less reliably than they once were. Your email platform counts an open when the mail app fetches a hidden image. Some apps and privacy tools now fetch that image before anyone reads the message, so the figure carries noise you cannot separate out. Use opens to compare two email subject lines sent on the same day to similar people, since the same noise affects both. Then judge the winner on clicks and replies, which sit much closer to the outcome you want.