Email subject lines that get opened, and the spam words to avoid
Spam filters do not reject email because of one scary word. They judge who you are, how you send and how people react. But the subject line decides whether people open, and that reaction is what builds or ruins your reputation.
Keep subject lines short and specific (about 4 to 8 words), write them like a person, not an advert, and avoid ALL CAPS, piles of exclamation marks, money symbols and fake "Re:" or "Fwd:". Single words like "free" rarely send an email to spam on their own; your setup, list quality and reputation matter far more.
What spam filters really check
- Who you are: whether your domain passes SPF, DKIM and DMARC, and your sending history.
- How people react: opens, replies, deletions without reading, and above all "Report spam" clicks.
- Your list: bounces from bad addresses and hits on spam traps.
- Content patterns: aggressive sales language stacked together, misleading subject lines, and suspicious links or attachments.
So a spotless subject line on a badly set-up domain still lands in spam, and an ordinary word like "free" in an email from a trusted sender is fine. Check your setup with the free DMARC and SPF checker.
Spam words and habits to avoid
| Type | Examples | Try instead |
|---|---|---|
| Hype | free!!!, guaranteed, risk-free, 100% satisfied | included, proven, no charge (once, in context) |
| Fake urgency | act now, urgent, expires today, hurry | available until Friday, ending soon |
| Money bait | cash, earn $$$, double your income, million | save time, lower costs, more orders |
| Pushy commands | click here, buy now, call immediately | see the details, reply with a time |
| Formatting | ALL CAPS, !!!, $$$, %%% | Normal sentence case, one punctuation mark |
| Tricks | Re: or Fwd: on a first email, "unsubscribe" in the subject | An honest description of the email |
One of these on its own rarely matters. Several together, from a sender with a weak reputation, make spam far more likely. Paste your email into a spam-word checker before a big send to catch them.
How to write a subject line people open
- Be specific. "Your March invoice from Sunny Bakery" beats "Important update."
- Keep it short. Phones cut subject lines off after roughly 30 to 40 characters, so put the key words first.
- Ask a real question when it fits: "Can we move Thursday's call to 3pm?"
- Use their name or company when you genuinely know them, not as a trick.
- Match the email. A subject line that promises something the email does not deliver earns spam reports.
- Say it out loud. If it sounds like a TV advert, rewrite it.
Before and after
| Before | After |
|---|---|
| URGENT!!! SAVE BIG ON BRAKES | A reminder about the brakes on your F-150 |
| FREE consultation - ACT NOW | Free 20-minute roof check this week? |
| New features available now!!! | New reporting tools for your team |
| Re: our conversation (with no conversation) | Quick question about your listing on Maple St |
| You won't believe this | The pricing mistake costing you sales |
Subject line examples by situation
| Situation | Example |
|---|---|
| Invoice or receipt | Invoice #1042 from Sunny Bakery, due May 30 |
| Follow-up | Following up on Tuesday's quote |
| Meeting | Can we meet Thursday at 10? |
| Newsletter | October tips: 3 ways to cut your heating bill |
| Cold email | Question about Gulf Coast Supply's deliveries |
| Job application | Application: Marketing Assistant, Jordan Lee |
More on writing the email itself: how to write an email.
The bigger fixes that keep you out of spam
- Set up SPF, DKIM and DMARC on your domain.
- Remove bad and risky addresses before you send: see how to clean an email list.
- Send in steady batches, not one giant blast.
- Make unsubscribing easy. An unsubscribe is far better for you than a spam report.
- Follow the email deliverability checklist.
Questions people ask
- Does the word "free" send email to spam?
- Not on its own. Filters look at your reputation and setup first. "Free" combined with all caps, exclamation marks and money symbols, from an unknown sender, is what gets flagged.
- How long should an email subject line be?
- Short enough to read on a phone: about 4 to 8 words, with the most important words first.
- Should I use emojis in subject lines?
- One relevant emoji can work for newsletters. Avoid them in business, cold and transactional email, and never use several.
- Does putting "unsubscribe" in the subject help?
- No. It makes the email look like spam. Put a clear unsubscribe link in the email instead.