Spam Words and Spam Checkers: How to Write Emails That Don’t Land in Spam

1 out of 6 legitimate marketing emails never makes it to the inbox. (Source: 2023 Email Deliverability Benchmark, Validity)

Why? Just because a word, a phrase, or even a simple sentence triggered a spam filter.

Unfair? Totally. But that’s how it works.

In this article, we’ll break down:

• Which words can get you flagged.

• Why they’re hurting your deliverability.

• And most importantly, how to stop shooting yourself in the foot with your emails—without losing your message’s impact.

What Is A Spam Word?

A spam word is a term or phrase that triggers spam filters because it’s statistically linked to unwanted content. Classic examples? "free," "win," "urgent," "click here," or "limited time offer."

Selling a product isn’t spam. But making over-the-top promises with vague phrases is.

For example:

• A solid marketing message: “Discover how our solution helps you save time every day.”

• Pure spam: “Limited time! Act now to WIN BIG with our secret formula!”

It’s all about context, wording, and intent. You can sell without sounding like a used car salesman.

Spam words don’t just tank a single email—they can trash your sender reputation.

The more often your emails trigger filters or get ignored, the lower your sender score drops.

And once your reputation takes a hit, it sticks to you like bad breath—hard to get rid of, and it’ll hurt all your future sends.

How Do Spam Filters Actually Work?

Spam filters don’t just scan for words. They’re like hyper-vigilant bouncers checking everything:

• Content: words, phrases, HTML structure, attachments.

• Technical setup: IP address, sending domain, authentication (DKIM, SPF, DMARC).

• User behavior: opens, clicks, spam reports, deletions.

• Sending history: if you’ve sent spam before, it’s on your record.

Forget static “banned word” lists—those days are over. Today, AI runs the show.

The algorithms learn from user behavior:

👉If too many people mark your email as spam, next time it’s more likely to go straight to junk.

👉If your email gets opened, clicked, or engaged with, it has a better chance of reaching the inbox.

Every email is scored in context, in real time, and based on your sender history. The AI is always adapting. Trying to “game” the system? Bad idea. Your best bet: keep it clean, clear, and relevant.

Top 100 High-Risk Spam Words and Their Safer Alternatives

Let's be clear: there's no definitive list of spam trigger words.

In 2025, it's not just about individual words but the context in which they're used. For instance, "free" might be acceptable in an informational email, but when combined with phrases like "act now" and "click here," it's a surefire way to land in the spam folder.

However, certain terms remain high-risk due to their historical and statistical association with spam. Here are some examples, along with concrete explanations. Use them sparingly and, most importantly, in the right context.

E-commerce & Retail

In the e-commerce sector, many terms seem essential (like "free shipping" or "discount"), but when overused or presented without context, they trigger spam filters. The issue often lies in the accumulation of these words in overly aggressive or urgent phrases.

Finance & Investment

Certain terms are statistically linked to financial scams. Spam filters and email providers closely monitor these phrases, as they're often used by unscrupulous actors.

Health & Wellness

The health sector is highly sensitive when it comes to spam filters. Why? Because it's been (and continues to be) a favorite playground for spammers: fake miracle pills, magic diets, dubious remedies.

B2B & Professional Services

In B2B, it's tempting to sell dreams: promises of guaranteed results, rapid growth, exclusive opportunities... But that closely resembles what spammers promise. Filters don't distinguish between a well-intentioned message and a scam, so caution is advised.

Education & Training

In this sector, the challenge is often to spark the desire to learn, but be careful: some expressions give the impression of clickbait or false promises. Spam filters are vigilant, especially if you promise freebies or overly easy results.

Real Estate

Real estate has attracted spammers for years: promises of dream homes, unconditional financing, urgent offers... As a result, certain expressions are closely monitored by filters because they've been massively used in dubious campaigns.

6 Rules to Avoid Spam Words and Keep Your Emails Impactful

Respect the Rules (CAN-SPAM, GDPR, etc.)  

Before you even think about the words you use, there’s a non-negotiable rule: follow the law.

If your email doesn’t comply, it will be flagged as suspicious—or blocked entirely.

The bare minimum for every marketing email:

✅ A clear, functional unsubscribe link.

✅ The sender’s identity (your real name and a valid physical address).

✅ A legitimate reason for contacting them (prior opt-in or an existing business relationship).

In the U.S., it’s all about CAN-SPAM. In Europe, it’s GDPR. The details vary, but the core principle is the same: No consent = no email.

👉 Don’t panic—here’s our deep dive on the topic: “Follow Regulations and Best Practices.”

Spotlight on Double Opt-In: It’s Easier Than You Think.

Here’s how it works:

• The user signs up for your list.

• They get a confirmation email.

• They click a link to confirm their subscription.

It might seem like a hurdle, but it’s the best filter to keep your list clean and engaged—with people who actually want to hear from you.

Clean Your Contact Base Regularly  

Your email list is like a garden: if you don’t weed it, it turns into a mess fast.

Here’s what you need to do:

• Remove invalid addresses (hard bounces, permanent errors)

• Cut out chronically inactive contacts (people who haven’t opened or clicked in ages)

• Flag risky addresses (role-based like sales@, info@, support@...)

• Fix obvious typos (like gmial instead of gmail)

💡 Pro tip: Schedule a list cleaning session every 3–6 months, or after any major campaign.

 Control the Frequency and Timing of Your Emails

Send too often, and you’re annoying. Send too little, and you’re forgotten. The key is consistency. Pick a cadence—weekly, biweekly, monthly—and stick to it. Your audience gets used to it, and so do the filters.

💡 Pro tip: For B2B or deep-dive content, one email every 2 weeks can be enough. For B2C (ecommerce, news), aim for 1–2 emails per week max. Test. Measure. Adjust.

Personalize Your Messages to Boost Engagement

Personalization isn’t just adding someone’s name in the header. It’s about:

• Tailoring the content based on the profile: loyal customer or new lead?

• Considering behavior: have they clicked on a link? Opened your last 3 emails?

• Segmenting your audience to send the right message at the right time.

Start simple: first name + recent context.

Example:

❌ "Check out our new offer."

✔️ "John, your last purchase qualifies you for an exclusive discount."

💡 Pro tip: Use dynamic tags in Mail Merge for Gmail (like {{first_name}}, {{last_purchase}}).

👉 We’ve compiled our best tips here: “How to write a cold email”.

Write Clear and Honest Subject Lines and CTAs

Overpromising in your subject line or CTA (like "Win $10,000 effortlessly!") triggers immediate red flags for spam filters. Before hitting send, ask yourself two simple questions:

• If I received this email, would I immediately understand what it’s about?

• Does it sound like a realistic offer—or too good to be true?

👉 Need inspiration? Check out our guide:  “How to write a Cold Email Subject Lines that convert”. 

These "best practices" to avoid — at all costs  

Some “hacks” keep circulating in cold emailing and marketing circles, often sold as magic tricks to bypass spam filters. Spoiler: they’re bad advice that will tank your deliverability.

Using Images To Hide Spam Words 

The idea: “I’ll hide sensitive words (like free, buy, click here…) inside images, so filters won’t catch them.”

The problem: Spam filters are highly suspicious of emails with more images than text. Why?

Because it’s a classic spammer tactic from way back.

Hiding Text In Html Code  

The idea: “I’ll add white text on a white background, or hide it inside a div (with display:none), to boost deliverability without anyone noticing.”

The problem: That’s pure black hat—and a huge red flag for spam filters.

Using Weird Or Broken Synonyms  

The idea: “I’ll write ‘Fr€€’ instead of ‘Free’ or ‘Cl1ck H3re’ instead of ‘Click Here’ to trick the filters.”

The problem: These sloppy substitutions are easily detected by modern filters.

Believing Content Alone Is Enough  

The idea: “If I avoid spam words, I’m safe—even if I blast thousands of emails to an old list.”

The reality: Filters don’t just look at your content. They analyze:

• Your sender reputation (domains, IPs)

• Your engagement rates (opens, clicks, spam reports)

• Your list quality (bounces, unsubscribes)

• Your sending frequency and volume

Bottom line: Content matters, but it’s not enough. You can have a perfect email, but if your tech stack and list hygiene are a mess, you’ll still land in spam.

Are free spam checkers worth it for testing your emails?

Even if you’ve polished your content, subject lines, and list, there’s one last step you must not skip: testing your emails before you hit send. But are free tools any good? In a word: they’re useful, but limited.

✅ Pros

Free tools like Mail-Tester, MxToolbox, or the free version of GlockApps are good for basic checks:

• See if you’re on a blacklist.

• Catch simple issues (spam words, broken links, missing images).

• Check your SPF, DKIM, DMARC setup.

• Get an overall spam score for a first impression.

❌ Major limitations

• No multi-provider testing (Gmail, Outlook, Yahoo…) like GlockApps or Litmus offer.

• Don’t fully assess your domain or IP reputation.

• Can be too generic—a 10/10 score on Mail-Tester doesn’t mean you’ll land in the inbox if your domain is blacklisted elsewhere.

💡 Pro tip: Combine tools for a better picture—use Mail-Tester + MxToolbox + SenderScore for cross-checking.

Expert Tip: How To Avoid Spam With The Mail Merge For Gmail Add-On

If you’re using Mail Merge for Gmail—an add-on that works with Gmail and Google Sheets—you’ve already got a head start on staying out of spam. Here’s why Mail Merge for Gmail helps:

1. Emails are sent directly from your own Gmail account. No third-party servers, no sketchy platforms. You benefit from your Gmail sender reputation and avoid issues linked to shared IPs or shady sending domains.

2. Automatic delay between sends. Mail Merge adds a smart interval between emails. This prevents the dreaded “blast effect” (massive sends all at once) that filters often flag as suspicious.

Together, these features:

• Mimic natural human sending behavior.

• Reduce your risk of being marked as spam.

• Boost your overall deliverability.

FAQ

What are spam trigger words in Gmail?

In Gmail, spam trigger words are terms or phrases that, when detected, can activate spam filters and send your email straight to the junk folder. These often include overhyped promises, too-good-to-be-true offers, or phrases commonly used in scams.

What are 5 negative words to be avoided in emails?

Here are five words or phrases to avoid in your emails to keep them professional and positive:

1. Just – can minimize your message.

2. Sorry – can signal weakness or fault.

3. I think – shows lack of confidence.

4. Maybe – feels uncertain.

5. Actually – can sound condescending.

What is a spam example?

A typical spam email is an unsolicited message claiming you’ve won a prize or large sum of money, prompting you to click a link or provide personal information. These are often scams or phishing attempts.

Is there a complete list of words to avoid in emails?

No, there’s no universal, official list. But some guides, like the "100 spam words" lists, offer useful insights on terms commonly flagged by filters. Treat them as guidelines, not strict rules.

What tools can I use to check if my email has spam trigger words?

Use spam checkers like Mail-Tester, GlockApps, or Folderly. They analyze your emails and flag risky words or phrasing. Combine tools for a more complete diagnostic.

What words are particularly sensitive in email subject lines?

Words related to freebies, unrealistic promises, or artificial urgency often trigger spam filters:

Free, Limited time, Act now, Guaranteed, Urgent, Winner…

Also avoid overly generic phrases like "Special offer," "Exclusive deal," etc. Be specific and honest in your subject lines.

Can the word "offer" get my email flagged as spam?

Yes, in some cases. "Offer" isn’t inherently a spam word, but it’s risky because it’s often linked to aggressive sales tactics. Used with other sensitive terms ("Free," "Limited time") or in a heavily promotional context, it can trigger filters.

For the best chance at reaching the inbox, don’t just guess—test your emails. If you’re serious about deliverability, Mail Merge for Gmail is the smartest add-on you can use with Gmail.