Someone told you to never use "FREE" in your subject lines like we're still running spam filters from 2004. You've been tiptoeing around perfectly good words because a blog post from seven years ago said they'd send you straight to spam.
Here's what's actually happening: you're avoiding words that don't matter while ignoring the things that do. Modern spam filters don't work like banned word lists. They use machine learning trained on billions of emails to spot patterns, not individual words.
The word "free" isn't killing your deliverability. Your terrible sender reputation is.
The Truth About Spam Trigger Words
Most articles about spam trigger words give you a list of 200+ words to avoid and call it a day. Completely useless.
Gmail and Yahoo don't maintain a master list of forbidden words. They use sophisticated machine learning models that analyze hundreds of signals simultaneously. The word "free" in your subject line? That's one data point among thousands.
Context matters infinitely more than the word itself.
A legitimate brand email: "Get free shipping on orders over $50"
A spam email: "FREE VIAGRA NO PRESCRIPTION NEEDED"
Same word. Totally different context. One gets delivered. One gets nuked.
Your sender reputation, authentication setup, and engagement history determine whether that word helps or hurts. The spam filter already knows if you're trustworthy before it even reads your subject line.
Think of it like airport security. TSA doesn't just look at your shoes. They check your boarding pass, your ID, your ticket history, behavioral patterns, and a dozen other signals. One element alone doesn't get you flagged. It's the combination.
Words That Actually Raise Red Flags
Some words do tend to correlate with spam. But correlation isn't causation.
These words show up frequently in spam emails because scammers use them, not because the words themselves are banned. When you combine them with poor sender reputation and sketchy sending patterns, you've got a problem.
| Category | Examples | Why They're Risky |
|---|---|---|
| Money/Financial | Cash bonus, earn $$$, make money fast, double your income | Used heavily in financial scams and get-rich-quick schemes |
| Urgency Pressure | Act now, expires today, only 3 left, urgent response needed | Classic manipulation tactic spammers use to force quick action |
| Too-Good-to-Be-True | Miracle cure, lose 30 lbs overnight, guaranteed winner | Red flag for medical scams and fake product claims |
| Shady Business | No credit check, hidden fees, offshore account, MLM | Associated with financial fraud and pyramid schemes |
| Excessive Symbols | !!!, $$$, 100% FREE!!!, CLICK HERE NOW!!! | Screams desperation and low-quality marketing |
Using "earn extra income" in an email from your verified business domain with a strong sender reputation? You're probably fine.
Using "EARN $$$ FAST NO EXPERIENCE!!!" from a brand new domain with zero engagement history? You're getting filtered instantly.
See the difference?
What Matters More Than Word Choice
Want to actually improve your deliverability? Stop obsessing over word lists and fix the fundamentals.
Your Sender Reputation Is Everything
Mailbox providers track your behavior over time. Every bounce, spam complaint, and unopened email damages your reputation. Every positive engagement builds it back up.
A sender with excellent reputation can use "risky" words and still land in the inbox. A sender with terrible reputation gets filtered even with perfect copy.
Recent data shows that sender reputation accounts for approximately 80% of deliverability decisions. Content analysis (including word choice) makes up maybe 20%. You're optimizing the wrong variable.
Email Authentication Actually Works
Set up your SPF, DKIM, and DMARC records correctly. This proves you're actually authorized to send from your domain.
Spam filters give authenticated senders significantly more benefit of the doubt. Skip authentication and your emails are suspicious before anyone reads the subject line.
Engagement Rates Tell the Real Story
Gmail watches what people do with your emails. High open rates, clicks, replies, and forwards signal that subscribers want your content. Low engagement or instant deletes? Red flag.
This is why list hygiene matters so much. Sending to dead addresses and disengaged subscribers tanks your metrics, which tanks your deliverability.
You can write the most innocent subject line in the world. If nobody opens your emails, spam filters will start routing you to promotions or spam regardless.
Technical Setup Matters
Beyond authentication, make sure your technical foundation is solid:
- Use a dedicated sending IP for high volume
- Maintain consistent sending patterns (don't spike from 1,000 to 100,000 emails overnight)
- Monitor your bounce rates religiously
- Implement proper unsubscribe links (required by law anyway)
- Warm up new sending domains properly with email warmup protocols
These factors collectively have far more impact than avoiding the word "discount" in your subject line.
How to Use "Risky" Words Safely
Sometimes you legitimately need to use words that appear on spam trigger lists. Here's how to do it without destroying your deliverability.
Match your brand voice. If you're a B2B SaaS company, "miracle solution" sounds fake. If you're an established retailer, "50% off sale" is completely normal.
Test everything. Use email testing tools to check spam scores before sending. Tools like Mail Tester give you a deliverability preview.
Build trust first. New senders should avoid aggressive promotional language until they establish positive engagement patterns. Earn your reputation before pushing boundaries.
Use plain language. Instead of "ACT NOW LIMITED TIME OFFER," try "Sale ends Friday." Same urgency, less spam energy.
Avoid ALL CAPS and excessive punctuation!!! Even safe words look spammy when you yell them with multiple exclamation points.
Context and delivery matter more than the individual words. A well-designed email from a trusted sender can include promotional language without issues.
The Real Deliverability Killers
Want to know what actually destroys your inbox placement? It's not spam trigger words.
Purchased or Scraped Email Lists
This is the fastest way to tank your sender reputation. You're sending to people who never asked for your emails. Spam complaints skyrocket. Engagement drops to zero. Spam filters notice immediately.
Never, ever buy email lists. Build your list organically with proper double opt-in processes.
Sending to Inactive Subscribers
That person who hasn't opened an email from you in 14 months? Stop sending to them. They're dragging down your engagement metrics.
Implement sunset policies to remove chronically disengaged subscribers. Your deliverability will improve when you focus on people who actually want your emails.
Ignoring Email Authentication
We mentioned this already but it deserves repeating. No SPF, DKIM, or DMARC? Your emails are fighting an uphill battle from the start.
This is table stakes for professional email marketing. Set it up correctly or accept that a significant portion of your emails will get filtered.
Inconsistent Sending Patterns
Sending 50,000 emails after months of silence triggers spam filters. Erratic volume patterns look suspicious.
Maintain consistent sending schedules. If you need to increase volume, ramp up gradually over weeks, not overnight.
Poor List Hygiene
Hard bounces, spam traps, and invalid addresses poison your sender reputation. Clean your list regularly. Remove bounces immediately. Use email list segmentation to target engaged subscribers.
Dirty lists are the number one reason good senders end up in spam. Fix this before worrying about subject line wording.
FAQ
Is "free" a spam word?
No. "Free" appears in millions of legitimate marketing emails every day. The word itself won't trigger spam filters if you have good sender reputation and proper authentication. The problem is when "free" appears alongside other spammy patterns like all caps, excessive punctuation, or from an unverified sender.
Do spam filters scan email content?
Yes, but content is only one factor among many. Modern spam filters use machine learning models that analyze sender reputation, authentication, engagement history, sending patterns, and hundreds of other signals. Content analysis happens, but it's weighted much lower than sender behavior and subscriber engagement.
Can I use urgency in subject lines?
Absolutely. Urgency is a legitimate marketing tactic when used appropriately. "Sale ends Sunday" or "Last chance for early bird pricing" are fine. The problem is fake urgency combined with other spam signals like "ACT NOW BEFORE IT'S TOO LATE!!!" from an unknown sender.
What words should I never use in emails?
There's no universal never-use list. Context, sender reputation, and email design determine deliverability more than individual words. That said, avoid combining multiple high-risk elements: all caps, excessive punctuation, money symbols ($$$), and aggressive claims in the same email.
How do spam filters actually work in 2026?
Modern spam filters use machine learning trained on billions of emails. They analyze hundreds of signals including sender reputation, authentication (SPF/DKIM/DMARC), engagement patterns, sending behavior, content, links, images, and subscriber interaction history. They don't use simple word blacklists. They spot patterns that correlate with spam behavior.