Email Subject Lines: How to Write Ones People Actually Open

Your subject line is the one part of an email that every subscriber sees. Before anyone reads your carefully written newsletter or clicks your offer, they glance at a short line of text in a crowded inbox and decide, in a second or two, whether to open, save for later, or ignore. This guide covers the principles behind subject lines that earn the open honestly, how preheader text and mobile screens change the picture, what to avoid, and how to test. It finishes with more than 30 example lines you can adapt.

What a subject line needs to do

A good subject line answers one question for the reader: “Why should I open this now?” It does that by being:

• Recognizable. Paired with a sender name people know, it signals that this is an email they asked for.
• Clear. The reader understands what is inside.
• Relevant. The topic matters to them, not just to you.
• Honest. The email delivers what the subject line promises.

That last point matters more than it seems. A clever subject line that oversells might win one open, but readers remember the disappointment. Over time, misleading lines lead to fewer opens, more unsubscribes, and more spam complaints, which can also hurt your deliverability.

Core principles

Clarity beats cleverness

When in doubt, say what the email is about. “Your March class timetable” is not exciting, but it is immediately useful to someone who goes to your classes. Puns and wordplay can work for some brands, but if the reader has to decode the line, many will not bother.

A quick test: could a subscriber guess the main content of the email from the subject line alone? If yes, you are on solid ground.

Specificity beats vagueness

Specific details make a line more believable and more useful. Compare:

• “Some tips for your garden” vs “3 jobs to do in the garden before the first frost”
• “News from us” vs “We now open at 7am on weekdays”
• “Big sale” vs “20% off all notebooks until Sunday”

Numbers, names, dates, and concrete outcomes all help. Just make sure every detail is accurate.

Curiosity, done honestly

Curiosity is a powerful reason to open, but it should come from the content, not from withholding basic information. A line like “The mistake I made with my first 100 subscribers” creates curiosity and is honest, because the email explains the mistake. A line like “You won’t believe this…” creates curiosity but tells the reader nothing and often feels like clickbait.

A useful balance is to be clear about the topic and leave the detail for inside: “Why our sourdough takes 48 hours (and why it’s worth it).”

Write for one reader

Subject lines that sound like a person talking to a person tend to feel more inviting than ones that sound like a press release. “Quick question about your Saturday booking” reads differently from “Important Update Regarding Your Reservation.”

Preheader text: the second subject line

Most email apps show a line of preview text after or below the subject line. This is the preheader. If you do not set it, many apps pull the first text in your email instead, which might be “View this email in your browser” or an image description.

Use the preheader to add information the subject line could not fit:

Subject line	Preheader
Your autumn timetable is here	Two new evening classes and a beginners’ course from October 6
20% off all notebooks until Sunday	Including the dotted grid ones that sold out last time
We moved!	Same team, new address two streets over, and parking out front

Avoid repeating the subject line word for word. Think of the two together as a short headline and subheading.

Length and mobile screens

Many people read email on a phone, where the visible part of a subject line is short. The exact cutoff depends on the device, app, screen size, and font settings, so there is no single magic number. A practical approach:

• Front-load the important words. Put the key information in the first few words.
• Check that the line still works when truncated. “20% off all notebooks until Sunday” still makes sense if it is cut to “20% off all notebooks…”.
• Preview before sending. Send a test to your own phone and look at it in the inbox, not just inside the email.

Main point

In the first few words

Preheader

Set it, and add new information

Truncation

Still makes sense if cut short

Honesty

The email delivers the promise

Formatting

No all caps, few or no exclamation marks

Personalization: useful, not gimmicky

Most email tools let you insert a subscriber’s first name or other details into the subject line. Used carefully, this can make an email feel more personal. Used carelessly, it can feel automated or even awkward.

Some guidelines:

• Personalize with relevance, not just names. “New yoga classes near Riverside” based on a subscriber’s location or interest is often more meaningful than “Anna, check this out.”
• Always set a fallback. If a first name is missing, the line should still read naturally (“Hi there” rather than “Hi ,”).
• Do not overuse it. If every email uses the subscriber’s name, it stops being noticeable.
• Check your data. Names typed in all caps or with typos will show exactly as stored.

Segmenting your list by interest or behavior lets you write subject lines that fit each group. Our email list segmentation guide explains how.

What triggers spam filters and mistrust

There is a lot of folklore about “spam trigger words.” Modern spam filters look at many signals together, especially your sender reputation, your email authentication setup, and how recipients interact with your messages. A single word like “free” will not, on its own, send a legitimate email to spam.

That said, some habits look untrustworthy to filters and to people:

• ALL CAPS and multiple exclamation marks!!!
• Fake reply or forward prefixes, like “Re:” or “Fwd:” on an email that is not a reply. This is deceptive and, in some jurisdictions, misleading subject lines can also raise legal issues.
• False urgency, such as “Last chance” when it is not.
• Misleading claims about the content, prices, or what the reader has won.
• Excessive symbols like $$$, or lots of emojis in a row.
• Vague alarm, like “Your account” or “Action required,” from a marketing sender. These resemble phishing emails.

A/B testing subject lines

Many email platforms, including MailerLite on all of its plans, let you A/B test subject lines. Typically the tool sends two (or more) versions to a portion of your list, waits a set time, and sends the better-performing version to everyone else.

To get useful results:

1. Test one idea at a time. For example, a question vs a statement, or with a number vs without. If you change three things at once, you will not know which mattered.
2. Decide what “winning” means. Opens are the usual measure for subject lines, but because privacy features in some email apps make open data less reliable, also look at clicks where your tool allows it.
3. Use a large enough test group. With a very small list, differences between versions can easily be down to chance. If your list is small, treat results as hints rather than proof.
4. Write down what you learn. Keep a simple log of tests and outcomes. Patterns over several sends are more reliable than one result.

See our email marketing metrics guide for more on reading the numbers.

Example subject lines by situation

The lines below are examples written for this guide, not proven winners. Use them as starting points and adapt them to your audience, your voice, and the actual content of your email.

Regular newsletters

1. “This month: 3 things worth your time”
2. “What we learned from fixing 40 leaky taps”
3. “Your October reading list (5 short picks)”
4. “The question I get asked most, answered”
5. “Behind the scenes: how we test a new recipe”
6. “Small wins, a new face, and a winter tip”
7. “Issue 24: the case for shorter meetings”

Product or service launches

8. “New: evening classes start October 6”
9. “It’s here: the canvas tote you asked for”
10. “Introducing our 30-minute express service”
11. “Now booking: spring garden makeovers”
12. “We built this because you kept asking”
13. “First look for subscribers: our winter menu”

Events and webinars

14. “You’re invited: open studio, Saturday 2pm”
15. “Free workshop: email basics for small shops”
16. “Tomorrow at 10am: your link to join”
17. “Starting in 1 hour (here’s the agenda)”
18. “Missed it? The recording is ready”

Re-engagement

19. “Still want to hear from us?”
20. “It’s been a while, here’s what’s new”
21. “Should we stop sending you emails?”
22. “Quick check-in: what would you like more of?”
23. “One click to stay on the list”

E-commerce

24. “Your basket is waiting (we saved your items)”
25. “Back in stock: the linen shirt in sage”
26. “20% off all notebooks until Sunday”
27. “Free shipping this weekend on orders over $40”
28. “How to care for your new leather bag”
29. “Thanks for your order, here’s what happens next”
30. “Picked for you: new arrivals in your size”
31. “Last day: winter sale ends at midnight”

For more on welcome sequences and their subject lines, see the welcome email sequence guide. If you sell online, our e-commerce email marketing guide covers automated emails like abandoned carts in more depth.

A simple process for every send

When you sit down to write a subject line, try this:

1. Finish the email first, so you know what the subject line has to represent.
2. Write five to ten options quickly, without judging them.
3. Cross out anything vague, misleading, or hard to understand.
4. Pick the clearest one and front-load the key words.
5. Write a preheader that adds new information.
6. Preview it on your phone next to your sender name.
7. If your list is big enough, A/B test your top two.

Subject lines improve with practice. Keep a swipe file of lines from your own inbox that made you open, note why they worked, and look back at your own best performers. Over time you will develop a feel for what your readers respond to. For the writing inside the email, continue with how to write a newsletter.