Spam Words in Email: How to Avoid Spam Filters and Increase Deliverability

Every marketer’s worst nightmare is working on a perfect campaign just for it to land in the spam folder. 

If you keep ending up in junk, it’s usually caused by one or more deliverability issues. One of the most common causes is email spam trigger words. However, modern spam filtering systems are far more complex than just a list of “banned” words.

Today’s email providers look at a range of signals before deciding where a particular message belongs. Content and word choice still matter, but so do other factors like sender reputation, authentication setup, and engagement metrics.

In this guide, we’ll look at how spam filters work, a list of spam words to avoid in your campaign, and what determines whether your emails finally reach the inbox.

What Is Spam and How Did We Get Here?

In most cases, email spam words are a set of keywords designed to grab attention or create some sense of urgency, typically for promotional purposes. 

The first recognizable email spam is generally traced to 1978. A marketing manager named Gary Thuerk sent an unsolicited promotional message to around 400 ARPANET users.

Actually, it worked well enough that the company made $13 million in sales. But the backlash was immediate. Gary Thuerk himself says:

“An ARPAnet representative called me up and chewed me out. He made me promise never to do it again.”

As email adoption grew, similar mass messaging tactics plagued inboxes. Businesses, affiliate marketers, and scammers started sending bulk emails promoting everything from questionable financial opportunities to miracle health products. By 2011, spam had grown to account for over 80% of all global email traffic.

The Rise of Anti-Spam Technologies

To protect users, email providers began developing systems to detect unwanted messages. Early spam filtering relied on relatively simple techniques such as keyword matching and blacklists. If an email contained certain phrases or came from a known spam source, it could be automatically blocked or sent to a junk folder.

Modern spam filters are far more sophisticated than the early systems that relied mostly on detecting spam keywords. 

How Do Spam Filters Analyze Content Today?

Today, email providers evaluate multiple elements at once before delivering your message to the inbox, spam folder, or just blocking it entirely. 

Content Analysis and Heuristic Filtering: Excessive capitalization, spammy word choice, misleading subject lines, suspicious formatting (like invisible HTML elements or overuse of exclamation marks), or an unusually high ratio of images to text. 

AI Detection: Instead of relying on static rules, machine learning models continuously adapt to new tactics used by spammers. For example, if a certain type of phishing message starts circulating widely, the system can quickly learn its patterns and block similar messages in the future.

User Behavior Signals: Spam filters analyze how your audience interacts with your emails (opened, deleted, marked as spam, replied).

Authentication check: Finds out whether your SPF, DKIM, and DMARC records are properly configured. 

We’ll look at these factors in detail later. You can also check out these practical steps on how to stop my emails going to spam.

Why Do Email Spam Words Still Trigger Filters?

Given how advanced spam filtering systems have become, it may seem surprising that spammy words can still affect your deliverability. The reason is that over the years, spam campaigns have frequently used certain phrases to promise unrealistic benefits. Because these patterns appear repeatedly in unwanted messages, filtering systems treat them as potential warning signals.

Also, context matters far more than it used to. For example, a trusted sender with strong engagement metrics may safely use promotional language in a newsletter, while a new or unknown sender using the exact same wording could raise suspicion.

Another thing to note here is that spam filters will rarely block an email just because it contains a single spam word. Instead, these words influence the overall risk score assigned to your message. If an email contains multiple suspicious elements, such as aggressive promotional language and poor formatting, the presence of spam words increases the likelihood of being filtered.

Common Examples of Spam Words

We’ve categorized common words that trigger spam filters. As mentioned above, using one or two of these words will not automatically send your message to the junk folder. However, you want to use them as sparingly as possible.

Also, keep in mind that this spam keywords list is not exhaustive. Creating a list of all the possible words is simply not doable, as spammers will always come up with new ones. 

Below is a list of spam words to avoid in email, or at least use with extra caution. 

Financial and money-related

• Cashback, fast cash, earn $, make $
• Free money, free cash, free offer
• Cash bonus, cash prize, earn extra cash
• Make money fast, double your income
• No fees, no hidden costs, no investment, risk-free
• Earn per week, guaranteed income, passive income
• Million dollar, billion dollar, financially free, get out of debt
• Lowest price, best price, cheapest

Urgency and pressure phrases

• Act now, act immediately, act fast
• Limited time offer, offer expires, today only, one time
• Don't delete, don't hesitate, don't wait
• Last chance, final notice, urgent, time sensitive
• Order now, buy now, call now
• While supplies last, only X left, this won’t last

Health and pharma-related

• Miracle cure, miracle results
• Lose weight fast, burn fat
• Anti-aging, look younger
• Medical breakthrough
• No side effects, 100% safe, guaranteed results

Promotional, prizes, and giveaways

• You've been selected, you're a winner
• Congratulations, claim your prize, click here
• Free gift, free trial, gift included
• Winner, jackpot, you won
• Exclusive offer, special promotion, deal of the day

How to Write Emails That Pass Spam Filters

Bypassing spam filters involves more than removing spam trigger words. In practice, everything from your content to email structure plays a part. 

1. Keep Subject Lines Honest and Specific

Filters have gotten very good at detecting the mismatch between a subject line and email content. It’s important that your subject line accurately reflects your message. 

Misleading lines or promotional words designed to trick the recipient into opening your mail can backfire. Not only that, but they are also a violation of anti-spam laws like the CAN-SPAM Act and GDPR.

Some best practices for writing subject lines include:

• Use personalization to improve engagement rate
• Avoid excessive use of all caps, emojis and exclamation marks
• Keep it short and clear, ideally under 50 characters

2. Send Personalized Email Content

Sending personalized messages signals to spam filters that you have a real relationship with the addressee. When you reference the recipient’s past behavior, your emails look different from a generic blast. Even basic personalization, such as a first name in the subject line or pretext, reduces the likelihood of being flagged and improves open rates.

3. Maintain Clean Formatting

Spam emails often contain unusual formatting, such as excessive capitalization or large blocks of colored text. Modern spam filters look for these patterns when evaluating messages.

To avoid getting flagged, keep your formatting style simple and readable:

• Use normal sentence capitalization
• Avoid excessive punctuation
• Maintain a healthy balance between text and images (aim for 80:20 ratio)
• Use consistent fonts and spacing

This helps your message resemble a typical newsletter, not a flashy spam offer. The safe path is to write like a real person and avoid any aggressive design choices.  

4. Use Links Sparingly

Emails that contain too many links, shortened URLs, or links pointing to suspicious domains will also be flagged by filtering systems. It’s best to add only a few relevant links that lead to trustworthy domains. Make sure the link text matches the destination and avoid disguising links with misleading anchor text. For CTA buttons, add a matching alt text.

5. Include an Unsubscribe Button

When a recipient doesn’t find a clear unsubscribe option, they might mark your message as spam instead. This, in turn, severely damages your sender reputation. Adding a clear way for people to unsubscribe is also a legal requirement under the CAN-SPAM Act and GDPR. 

Why Avoiding Spam Words Alone Is Not Enough

Avoiding obvious spam words can help reduce risk, but it does not guarantee that an email will reach the inbox. From what we’ve seen, deliverability depends less on individual spam trigger words and more on the overall credibility of the sender. This means you should take other factors like sender domain and  IP reputation, engagement rate, and email authentication very seriously.

What is sender reputation, and why is it crucial?

Sender reputation is a combined score of your IP and domain reputation. Mailbox providers track the history of the domains and IP addresses that send email and use that information to estimate how trustworthy each sender is.

Reputation scores are influenced by several signals, including spam complaints, bounce rates, sending consistency, and recipient engagement. Senders that frequently generate complaints or send large volumes of unwanted email develop a poor reputation, which increases the likelihood of getting blocked or sent to spam.

Domain Reputation or IP Reputation: Which Matters More?

Both domain and IP reputation are equally important for deliverability. However, they serve different functions.

IP reputation is tied to the history of the specific server you use to send email. Key factors that influence your reputation are bounce rates, spam complaints, engagement metrics, and authentication pass rates.

On the other hand, your domain reputation reflects your sending domain (“From” address) rather than your IP address. Some factors that impact your score here include website authority, domain history, DMARC policy compliance, DKIM signature consistency, and cross-channel reputation signals.

If you’re unsure whether to focus on domain reputation or IP reputation, protecting your domain should be the priority. While mailbox providers still consider both, they put more emphasis on domain reputation. You can switch IPs, but you can't easily escape a damaged domain reputation. 

The Role of Email Authentication Protocols (SPF, DKIM, DMARC)

Email authentication helps mailbox providers verify that a message was actually sent by the domain it claims to come from and was not altered while in transit. Without proper authentication, emails are more likely to be filtered or rejected.

Three main email authentication protocols every sender should have configured are:

• SPF (Sender Policy Framework): This specifies which IP addresses are authorized to send email on behalf of your domain. When a receiving server checks your email, it looks up your DNS SPF record to verify that the sending IP is on the approved list.
  
  
• DKIM (DomainKeys Identified Mail): DKIM adds a cryptographic signature to your emails that proves the message wasn't altered in transit. It confirms the message originated from your domain, which is specified in its envelope headers.
  
  
• DMARC (Domain-based Message Authentication, Reporting and Conformance): This builds on SPF and DKIM by telling receiving servers what to do if an email fails authentication checks. This could be to deliver it, quarantine it, or reject it outright. It also provides reporting so you can find out if someone is sending emails using your domain name.

Together, these protocols help mailbox providers detect spoofing and phishing attempts while improving trust in legitimate emails. 

Engagement Metrics and List Hygiene

We’ve already mentioned that mailbox providers closely monitor how recipients interact with your emails. Positive engagement indicates that messages are relevant to the audience, while negative signals suggest that your emails may be unwanted.

List hygiene is therefore essential for maintaining healthy engagement metrics. Sending emails to inactive users leads to poor interaction and higher complaint rates.

To maintain good deliverability, regularly remove inactive subscribers, strictly avoid buying or renting email lists, and ensure recipients have clearly opted in to receive messages. Remember, your domain reputation is easy to spoil but much more difficult to restore.

Domain and IP Warm-Up Practices

New domains and IP addresses have little or no sending history. If you send large volumes of email immediately, mailbox providers may treat the activity as suspicious.

Warming up a domain or IP means gradually increasing your sending volume over time, usually for a period of 4 to 8 weeks. Start with low volumes (less than 1000 emails per day is safe) and increase gradually over time. This allows mail providers to observe normal engagement patterns and build trust in your sending domain or IP address.

How to Test Whether Your Emails Go to Spam

Testing emails before sending helps prevent formatting errors, broken links, and deliverability issues that can hurt campaign performance.

Start by sending test emails to yourself and a few team members to check how the message appears on different devices and email clients. Verify that subject lines, preview text, images, and links display correctly.

You should also validate your email list before sending. Email validation tools check whether addresses are real and capable of receiving messages. This helps catch typos, disposable addresses, or inactive domains before they cause bounces. 

Conclusion 

Getting emails into your recipient’s inbox is more complex than it used to be. You can write a solid message and still end up in spam if the surrounding signals are not in your favour.

Spam words are part of the picture, but they’re far from the whole story. Filters now pay attention to sender reputation, authentication, engagement, and how people respond to your emails.

The good news is that deliverability is not random. Once you understand what influences it (as we’ve covered above), you can start making small, consistent changes that will improve your chances of landing in the inbox instead of the spam folder.

Related Services

These UniOne tools make email sending and deliverability easier to manage end-to-end:

• Email API Service for Developers: A flexible solution for sending transactional and marketing emails with strong deliverability control, authentication support, and performance tracking.
• Transactional Email Services: Designed for high-volume, time-sensitive emails such as receipts, alerts, and notifications, ensuring fast and reliable delivery.
• Email Validation API: Helps verify email addresses in real time to reduce bounces, improve list quality, and maintain a stronger sender reputation.
• Transactional Email Templates: Create clean, well-structured emails that are easier to read and less likely to trigger spam filters. 

Frequently Asked Questions (FAQs)

How can I check if my email will go to spam?

You can test emails using free or paid tools like Mail Tester, GlockApps, and Spam Checker. You can also send test messages to multiple inboxes before sending to your audience, and ensure your authentication protocols are set up. 

Can emojis in subject lines trigger spam filters?

Yes, excessive emoji use can increase your spam risk. Filters associate multiple emojis with the kind of aggressive, attention-grabbing tactics common in scam emails. If you want to use them, stick to one emoji maximum and use it to complement the text rather than replace it.

How do I avoid spam filters when sending emails?

Avoiding spam filters comes down to your technical setup, sender reputation, and content. Make sure SPF, DKIM, and DMARC are configured correctly, send only to opted-in recipients, and keep your list clean by removing inactive addresses. Avoid the most common words in spam emails and formatting patterns associated with spam, such as misleading subject lines, too many links, and poor text-to-image ratio.