Stop Using These Words in Your Emails – They’re Sending You Straight to Spam (Study)

Spam filters have become smarter — and stricter. Even well-meaning emails like yours can get blocked if you use the wrong words. ZeroBounce analyzed thousands of flagged messages to identify the top spam trigger words and what to say instead.

Top 10 Spam Trigger Words

Based on how likely they are to land your email in spam:

1. Viagra
   213% more likely to appear in spam than in regular emails. Still the undisputed king of spam trigger terms.
2. Click
   147% more likely to be in spam emails. Common in phishing attacks and outdated CTAs.
3. Money
   Frequently used in financial spam. Associated with scams and promises of fast cash.
4. Cash
   A classic red flag. Often paired with phrases like “earn cash” or “get cash fast.”
5. Bonus
   Heavily flagged in promotional emails. Spam filters associate it with misleading offers.
6. Offer
   Has a 53% higher chance of being in spam than in legitimate messages. Common in aggressive promotions.
7. Sex
   Ranks 7th in spam terms. Almost exclusively used in harmful emails.
8. Urgent
   Ranks 5th overall. Triggers filters due to its use in manipulative, high-pressure messages.
9. Winner
   81.5% more likely to appear in spam than in regular emails. Often found in lottery and prize scams.
10. Free
    Deceptive when paired with terms like “free money” or “free trial.” Frequently used in clickbait promotions.

Even legitimate emails can get trapped in spam filters

Recent data shows that spam emails comprise nearly 46% of all global email traffic in 2025, with experts projecting it could rise to 58 billion junk emails daily within the next four years. A new study by ZeroBounce analyzed flagged email databases to identify the words that are most likely to get your emails flagged as spam. 

Brian Minick, Chief Operating Officer at ZeroBounce, warns that even legitimate businesses can involuntarily hurt their ability to reach the inbox. “Most people think spam filters only affect scammers. But even non-malicious emails get trapped when they use outdated, deceptive, or emotionally loaded language,” the email marketing expert says.

Related: An outdated email list that bounces can also hurt your email deliverability. Check out our Email List Decay Report to see how fast email databases degrade – and how you can fix yours.

The research focused on words and phrases like “earn cash” and “no credit check,” which more than doubled the chance of landing in the spam folder. With spam frequency, ratio to non-malicious emails, and the category of the spam emails for which they are used, the study ranks the words that trigger email spam filters the most.

Adult-themed emails dominate spam folders

The most common spam emails are adult-themed, with a spam frequency of over 2.7K.

The word that flags the email as spam the most is ‘viagra’, and it is 213% more likely to be in a spam email than in a regular one. “Sex” ranks seventh, and has the lowest spam-to-ham rate, showing that it’s almost exclusively used in harmful emails and should be avoided.

Financial and marketing emails are a magnet for spam filters

Financial and marketing emails are under the biggest risk of being flagged as spam. The top 10 most common spam words include “click”, “offer”, and “deal,” which are used in promotional and commercial-related emails.

Despite being a common call to action, “click here” is now a trigger for phishing warnings in both email clients and browser extensions. “Click” ranks as the second most common word flagged as spam, and has a 147% higher chance of being harmful.

Instead, use contextual links within relevant phrases like “view pricing” or “download the report” to increase engagement and avoid algorithmic penalties.

Spam filters can see “Free” as a deceptive promo

“Offer” is used frequently in marketing emails, and it has the third-lowest spam-to-ham rate, meaning it has a 53% higher chance of being in a spam message. Phrases like “free money” and “free trial” are often used in deceptive promotions, making them favorites for spam classifiers.

A better approach is to highlight value without sounding too good to be true. For example, swap “free trial” with “30-day access, no payment required.”

Related: Did you know that 80% of consumers report an email as spam simply because it looks like spam? Learn how to make sure your emails look trustworthy.

Urgency words hurt your credibility

Expressions such as “limited time” or “act now” signal pressure tactics. “Urgent” is the 5th most common word flagged for spam, making it harder to send actual critical messages. Email marketing expert Brian Minick advises using data-driven urgency like “4 spots left” or “ends June 15” to balance persuasion with authenticity.

Clickbait words are risky

Often used to draw attention and boost open rates, now clickbait-sounding words are flagged by spam filters. The most common words from the category include “click”, “winner”, and “guaranteed”. They are often used in harmful emails, with “winner” having an 81.5% higher chance of appearing in spam rather than in a regular message.

Why email deliverability now depends on tone, intent, and trust

With over 40% of global email marked as spam, even small changes to your email content can mean the difference between reaching an inbox or getting blocked by spam filters.

“Email deliverability is no longer just about avoiding bad behavior,” says ZeroBounce’s Brian Minick. “It’s about aligning with how machines and people read tone, intent, and trust.”

Related: Read our Guide to Email Deliverability to learn how to land your emails in the inbox

Spam words summary: what you need to know

Here’s your TL;DR: These are the top red-flag words that could send your emails straight to spam. Keep them in check to protect your deliverability.

• “Viagra” is the #1 spam trigger word, with a 213% higher chance of landing in spam
• “Click” is 147% more likely to appear in spam than in legitimate emails
• Financial terms like “cash,” “money,” and “bonus” are heavily flagged
• Adult-themed emails dominate the spam folder
• Words like “offer” and “free trial” increase your risk—even in legit marketing emails
• “Click here” is outdated and flagged; use contextual CTAs instead
• Urgency phrases like “act now” and “limited time” drain credibility and trigger spam filters
• Clickbait terms such as “winner” and “guaranteed” are common in flagged emails
• Even non-malicious emails suffer if they use emotionally loaded or deceptive language
• Tip: Highlight value clearly, avoid hype, and rethink your calls to action

For brands, the takeaway is clear: every word counts – far beyond the subject line. 

How we did the research

To uncover the most common spam trigger words, ZeroBounce researchers analyzed publicly available datasets used to train spam filters — like Kaggle’s popular “Spam vs. Ham” corpora. These datasets contain thousands of labeled emails, helping us compare words found in spam versus legitimate (aka “ham”) emails.

First, the team cleaned and standardized the data. That meant removing short, meaningless words, converting everything to lowercase, and eliminating noise like numbers or symbols. From there, we focused on words that appeared frequently in spam and calculated how often they showed up compared to legitimate emails.

Each word was then categorized into one of seven types, including:

• Financial terms (e.g., “cash,” “bonus”)
• Clickbait (e.g., “winner,” “guaranteed”)
• Phishing-related language (e.g., “verify,” “password”)
• Adult content
• Urgency-driven language
• Marketing terms
• Other miscellaneous triggers

We used Python to run the analysis, including libraries like Pandas, Regex, and Jupyter Notebooks. The result? A ranked list of high-risk words based on how exclusive they were to spam — and actionable insights to help improve your email deliverability.

For questions or media inquiries about this study, please contact ZeroBounce’s PR Manager Corina Leslie at corina at zerobounce dot net.