On this page
- Key takeaways
- What a newsletter subject line has to do
- The rules that hold up
- Seven formulas that work for newsletters, with examples
- Do not waste the preview text
- Spam trigger words: what is true and what is myth
- Check your subject with our free subject line tester
- How to test subject lines without fooling yourself
- More examples by newsletter type
- Common mistakes
Key takeaways
- A subject line is a promise about what is inside. Accurate beats clever, and US law (CAN-SPAM) requires it to reflect the content.
- Mailchimp recommends no more than 9 words and 60 characters, no more than 3 punctuation marks and no more than 1 emoji.
- Put the important words first. Phones show fewer characters than desktops, so the end of a long subject often disappears.
- "Spam trigger words" matter less than most lists claim. Authentication, sender reputation and complaints decide inbox placement far more than any single word.
- Check each subject with our free subject line tester, then judge results by clicks and replies, not opens alone.
What a newsletter subject line has to do
In the inbox, your edition is three things: the sender name, the subject line and the preview text. The sender name answers "who is this?", the subject answers "what is it?", and the preview text answers "why now?". A newsletter subject line has an easier job than a sales email, because the reader already asked to hear from you. It does not need to trick anyone. It needs to tell a subscriber, in a glance, that this week's edition is worth their next five minutes.
I keep a burner email address only for subscribing to other newsletters, and scrolling that inbox is the fastest subject line lesson I know. The ones I open are specific. The ones I skip are vague ("Issue #42", "This week's update") or shouting.
The rules that hold up
Most advice on subject lines is opinion. A few rules come from published guidance and are worth following by default:
- Keep it short. Mailchimp recommends using no more than 9 words and 60 characters.
- Go easy on punctuation. Mailchimp suggests no more than 3 punctuation marks per subject line. Strings like "!!!" or "??" look like spam to readers and filters.
- One emoji at most. Mailchimp advises no more than 1 emoji at a time, used to add to words rather than replace them. Gmail's sender guidelines also warn against using emojis or non-standard characters to imitate graphic elements with intent to deceive.
- Be accurate. The FTC's CAN-SPAM guide says the subject line must accurately reflect the content of the message. Gmail says message headers and content should not be misleading or deceptive.
- Front-load the meaning. Inboxes cut long subjects, and how much they show depends on the app, the device and even the font size. Put the words that carry the message in the first half so the subject still works if the end is cut off.
Seven formulas that work for newsletters, with examples
These patterns suit an edition people signed up for. The examples are illustrations written for a hypothetical newsletter about AI workflows and small products, but the patterns transfer to any topic.
| Formula | Example | Use it when | Risk |
|---|---|---|---|
| The specific result | How I cut my weekly reporting to 20 minutes | The edition teaches something with a clear payoff | Only use numbers that are true |
| The plain topic | Pricing a small SaaS: what I would do again | Readers already trust you and the topic is the draw | Can read as flat if the topic is broad |
| The honest curiosity gap | The AI tool I stopped paying for | The answer is inside and worth knowing | Turns into clickbait if the payoff is weak |
| The question | Are you still writing prompts from scratch? | The question names a real habit or pain | Yes or no questions invite "no" and a skip |
| The list | 3 automations that run my Mondays | The edition really is a list | Overused; the items must be strong |
| The mistake | My worst launch email, annotated | You can show a real error and the fix | Needs a genuine lesson, not a humblebrag |
| The series label | Tool of the week: a better meeting recorder | You run a recurring section readers look for | The label eats characters; keep it short |
Notice what these have in common: each one could only be about one edition. If a subject line would fit any week, it is not doing its job.
Do not waste the preview text
The preview text (also called preheader) is the snippet most inboxes show after the subject. If you leave it empty, the inbox fills it with whatever comes first in the email, often "View in browser" or an image caption. Write it on purpose.
- Extend, do not repeat. Subject: "The AI tool I stopped paying for". Preview: "and the free setup that replaced it in an afternoon."
- Add the second reason to open. If the subject is the main piece, the preview can mention the extra: "Plus: a reader's template for weekly planning."
- Keep the promise consistent. The preview is part of the same claim, so it must be accurate too.
Spam trigger words: what is true and what is myth
Lists of hundreds of "spam trigger words" are popular, and most of them overstate the case. Modern inbox providers decide where your email lands mainly by who is sending it and how recipients react, not by scanning for single words. Gmail's published requirements are about authentication (SPF or DKIM for all senders, DMARC for senders of more than 5,000 messages a day to Gmail accounts), keeping reported spam rates below 0.3%, one-click unsubscribe for bulk senders, and not being misleading. Yahoo's requirements follow the same pattern.
That said, some wording still hurts, for two reasons: readers mark it as spam, and complaints damage your reputation. The patterns worth avoiding in a newsletter subject line:
- Money and prize claims. "Free money", "You have won", "Guaranteed income". Rarely honest in a newsletter.
- Pressure. "Act now", "Urgent", "Last chance" on an edition that is not time-limited.
- Fake conversation markers. "RE:" or "FWD:" on a message that is neither a reply nor a forward. That is misleading under both CAN-SPAM and Gmail's guidelines.
- ALL CAPS and stacked punctuation. Reads as shouting and looks like spam at a glance.
- Bait and switch. Any subject the content does not deliver on.
If your newsletter is going to spam even with clean subject lines, the problem is almost always setup or list quality, not wording. Meisa's guide to why emails go to spam walks through the usual causes in order.
Check your subject with our free subject line tester
Our free subject line tester covers the checks that are easy to forget late at night before a send. It runs client-side in your browser and checks:
- Length in characters and words, against the published guidance above.
- Mobile truncation, showing roughly where a phone inbox is likely to cut the line.
- Spam-style wording from the patterns listed in this guide.
- Capitals and punctuation, flagging all-caps words and stacked marks.
Be clear about what it is: a heuristic checker, not an inbox placement test. It cannot tell you whether a specific email will land in Gmail's primary tab, because that depends on your authentication, your sending reputation and your readers' behavior. Use it to catch obvious problems, then rely on your own results.
How to test subject lines without fooling yourself
Most platforms let you A/B test subject lines by sending two versions to a sample and the winner to everyone else. That is useful, with two cautions.
First, opens are a weak signal now. Apple's Mail Privacy Protection prevents senders from seeing whether a message was opened, so a share of recorded opens are machine activity, not people. When you compare versions, look at clicks and replies too.
Second, small lists produce noisy results. If your list is small, a single test tells you little. Keep a simple log instead: date, subject, clicks, replies. After a couple of months, patterns show up that no single test would reveal.
For a sense of scale, Mailchimp's published benchmarks, last updated in December 2023, put the average open rate across all industries at 35.63% and the average click rate at 2.62%. Your own trend matters more than either number.
More examples by newsletter type
Curated link newsletters
- The one link worth your Friday
- 5 reads on pricing, and one I disagree with
How-to and playbook newsletters
- A 4-step review process for AI-written drafts
- How to write a welcome email people reply to
News and analysis newsletters
- What this week's model release means for small teams
- The update that changes how you should send email
Personal essay newsletters
- Why I moved my newsletter to Substack
- What I got wrong about my first sponsor
To see how professionals handle subject lines week after week, subscribe to a few from our lists of the best marketing newsletters, the best SEO newsletters and the best AI newsletters, and read only their inbox view for a month.
Common mistakes
- Issue numbers as the whole subject. "Issue #42" tells a subscriber nothing about why to open this one.
- Writing the subject first. Write it last, once you know what the edition actually says.
- The same pattern every week. Even a great formula wears out. Rotate between two or three.
- Promising more than the edition delivers. One disappointing open costs you the next one.
- Ignoring the sender name. Use a name readers recognize, and keep it the same every week.
For the rest of the edition, see our guides on how to write a newsletter and how to start a newsletter.
FAQ
How long should a newsletter subject line be?
Mailchimp recommends no more than 9 words and 60 characters. Because phones show fewer characters than desktops, put the words that carry the meaning at the start so the subject still works if the end is cut off.
Do spam trigger words really send emails to spam?
Less than most lists suggest. Inbox providers weigh authentication, sender reputation and complaint rates far more heavily. Misleading or pushy wording still hurts, mainly because readers report it as spam, and Gmail asks senders to keep reported spam below 0.3%.
Is a subject line tester an inbox placement test?
No. A subject line tester, including ours, checks the line itself: length, likely mobile truncation, spam-style wording, capitals and punctuation. Whether an email reaches the inbox depends on your domain authentication, sending reputation and subscriber behavior.
Should I use emojis in newsletter subject lines?
Sparingly. Mailchimp advises no more than one emoji at a time, used to add to words rather than replace them. Gmail's guidelines warn against using emojis to imitate graphic elements with intent to deceive.
Should I put the issue number in the subject line?
Not as the whole subject. An issue number tells readers nothing about why to open this edition. If you use one, put it after a specific description, or leave it to the preview text.