There are certain words you shouldn't use within your email subject line if you want to pique people's interest while avoiding spam blockers.
It's one thing if you're sending a personal email, but if you're sending mass emails, you're not going to get very far if 90% of your messages get blocked as spam before they ever reach their intended recipient.
Let's get into our list of words to avoid in email subject lines, so you can stay miles away from the spam folder.
What Are Spam Trigger Words?
Spam trigger words are terms that email service providers flag as indicators of unwanted or fraudulent messages. Modern filters use machine learning to evaluate content patterns, sender reputation, authentication protocols, and engagement history, not just individual words.
No single word guarantees your email lands in spam. Context matters. An established sender with strong engagement can use words like "free" or "limited time" without issue.
But combine multiple trigger words with poor sender reputation, and your inbox placement drops fast.
Spam filters evaluate three primary signal categories:
Content signals: Words, formatting, links, and subject line structure
Reputation signals: Domain age, authentication protocols, complaint rates, and sending history
Engagement signals: Open rates, reply rates, spam reports, and deletion patterns
Understanding these dynamics helps you write subject lines that pass filters and actually get read.
The Complete List of Spam Trigger Words by Category
Spam words fall into distinct categories based on the tactics they're associated with. This list covers financial terms, urgency language, promotional phrases, scam signals, income claims, and free offers — all relevant to B2B outreach.
Financial and Money-Related Words
Almost everything associated with a dollar sign triggers filters. Financial language mimics fraud patterns, especially when combined with urgency or promises.
These terms damage deliverability and credibility. Spam filters catch them before they reach their destination.
Common financial trigger words include:
Money back
Get paid
Cash
Dollars
Price
Big bucks
Credit or Debit
Profit
$$$
Spam Word | Why It Triggers | Safer Alternative |
|---|---|---|
Make money | Associated with get-rich-quick schemes | ROI impact, revenue outcomes |
Cash bonus | Mimics lottery/prize scams | Performance incentive, results-based compensation |
$$$ or $ | Symbols signal mass promotional email | Reference specific value |
Urgency and Pressure Words
Urgency language mimics phishing and scam patterns. Filters flag artificial pressure. If you have a time-sensitive offer, be specific: "Your demo is scheduled for Thursday" beats "Act now before it's too late."
Common urgency triggers include:
Limited time
Get it now
Once in a lifetime
For new customers only
Offer expires
Deal ending soon
Today
Soon
Last Day
Friday before [holiday]
This is especially true for emails tied to shopping events like Cyber Monday, Black Friday, or Giving Tuesday. Open rates drop significantly when day names appear in subject lines.
Promotional and Sales Language
Generic promotional language signals mass email to filters. Terms like "incredible," "amazing," and "best" add no value and trigger spam scoring. Let your actual offer and content demonstrate value instead.
Common promotional triggers include:
Email marketing
Content marketing
Digital marketing
Direct marketing
Fantastic
The best
Perfect
Unbelievable
Wonderful
You will not believe your eyes!
Instead, provide actual content in your email that your readers will be interested in engaging with.
Scam and Overpromise Words
These phrases are high-priority filter triggers that signal fraud to algorithms and readers. Guarantee language, winner announcements, and risk-free promises are hallmarks of scam emails—even legitimate offers can't overcome this association.
Common scam triggers include:
Risk-free
Guaranteed
No catch
Winner
Congratulations
You've been selected
No obligation
100% satisfied
Earn and Income Claims
Income and earnings language triggers immediate spam flags. These phrases are associated with MLM schemes and work-from-home scams, making them toxic for B2B outreach.
Common income claim triggers include:
Double your income
Be your own boss
Increase revenue
Financial independence
Eliminate debt
Potential earnings
Free Offers and Discounts
"Free" alone won't doom your email if you have strong sender reputation and relevant content. But combining it with other trigger words increases spam risk significantly.
Common free offer triggers include:
100% off
Allowance
Gift included
Rebate
0 down
Free trial
No cost
Formatting Mistakes That Trigger Spam Filters
Beyond word choice, how you format your subject line matters. Certain formatting patterns are so strongly associated with spam that they trigger filters regardless of content.
Common formatting mistakes include:
ALL CAPS: This reads as shouting and mimics scam email patterns. Create emphasis through relevant content instead.
Excessive punctuation: Multiple exclamation marks signal desperation and damage credibility. (Check this out!!!!!!)
Emojis and symbols: A single, relevant emoji rarely causes problems. Strings of emojis or symbols like $$$ trigger filters, especially when combined with other spam signals.
How to Write Subject Lines That Avoid Spam Filters
Avoiding trigger words is table stakes. Writing subject lines that actually work requires a different approach.
Best practices for spam-free subject lines:
Keep it under 50 characters: Prevents truncation on mobile devices and improves readability. Shorter subject lines also force you to be specific.
Match subject to content: Misleading subjects increase spam complaints. If your subject promises a case study, your email better deliver a case study.
Be specific: Vague subjects signal mass email. "Q4 pipeline review" beats "Important update" every time.
Test before sending: Use spam checkers to catch issues before your email hits inboxes. Most email service providers include basic spam checking.
Personalize where possible: Dynamic fields like company name or role signal relevance. But only personalize if your data is accurate.
The goal isn't just inbox placement. It's engagement. Write subject lines that give recipients a reason to open, and spam filters will follow your lead.
How to Test Your Subject Lines Before Sending
Spam score checkers analyze subject lines against known trigger patterns before you send. Most email service providers include basic spam checking in their platforms. Dedicated deliverability tools offer deeper analysis.
What spam checkers evaluate:
Trigger word density and combinations
Formatting issues (ALL CAPS, excessive punctuation)
Character length and mobile truncation
Special character usage
Comparison against known spam patterns
Inbox placement testing takes this further. Seed list testing sends your email to test addresses across major providers (Gmail, Outlook, Yahoo) to see where it lands: inbox, promotions tab, or spam folder.
Testing catches obvious mistakes. But the best defense against spam filters is sending emails people actually want to receive.
Personalization: The Real Antidote to Spammy Subject Lines
The best way to avoid spam filters is to send relevant, targeted emails that recipients actually want. Generic mass emails get flagged. Personalized outreach gets engagement.
Accurate contact data, firmographics, and intent signals enable personalization at scale. When you know which accounts are actively researching solutions like yours, you can craft subject lines that speak to their specific needs.
ZoomInfo's GTM intelligence helps revenue teams identify high-intent accounts and surface the context needed for relevant outreach. Copilot, ZoomInfo's AI-powered assistant, helps sellers craft personalized emails that feel individually written, not mass-produced. Companies using this approach see improved response rates because their outreach is contextual, not generic.
Personalization isn't about inserting a first name merge field. It's about understanding what matters to your recipient and leading with that insight. When your subject line demonstrates you've done your homework, spam filters and human readers both respond positively.
Talk to Sales to learn how ZoomInfo helps you send fewer, better emails.
Learn more about ZoomInfo Copilot
Frequently Asked Questions
What Words Trigger Spam Filters Most Often?
Financial promises, urgency language, and scam phrases like "free," "guaranteed," and "act now" are common triggers. Modern filters evaluate context alongside individual words.
Do Emojis in Subject Lines Trigger Spam Filters?
A single, relevant emoji rarely causes problems, but strings of emojis or symbols (especially combined with other spam signals) can trigger filters.
How Long Should an Email Subject Line Be?
Keep subject lines under 50 characters. This prevents truncation on mobile devices and forces you to be specific.
Can I Use the Word "Free" in Email Subject Lines?
"Free" alone won't doom your email if you have strong sender reputation and relevant content, but combining it with other trigger words increases spam risk.
How Do Spam Filters Actually Work?
Modern spam filters use machine learning to evaluate multiple signals: content patterns, sender reputation, authentication records, and recipient engagement history.
Key Takeaways
Avoiding spam filters isn't about memorizing a list of banned words. It's about understanding how modern email filtering works and adapting your approach accordingly.
Key principles to remember:
Context matters more than words: Sender reputation and engagement history amplify or diminish content signals.
Personalization prevents spam flags: Generic mass emails trigger filters. Targeted outreach gets delivered.
Test before sending: Spam checkers catch mistakes before they damage your sender reputation.
Prioritize engagement over delivery: The goal is replies, not just inbox placement.
Avoid sending generic messages to everyone in your database. It's difficult with limited resources and pressing deadlines.
But segmenting your audience, personalizing your messaging, following email subject line best practices, and testing frequency improves open and click-through rates.
Talk to Sales to learn how ZoomInfo helps teams send relevant, targeted outreach that avoids spam filters and drives real engagement.