How to Avoid Spam Filters: 12 Best Practices

Spam filters help protect inboxes from unwanted or unsafe emails. These filters look for signs that an email may be spam and block it from reaching the main inbox. Sometimes, even emails from honest senders can end up in the spam folder. This can hurt email deliverability and stop people from seeing important messages. If you send newsletters, updates, or promotions, it is important to follow certain steps so your emails do not get filtered out.

What Is a Spam Filter?

A spam filter is a tool used by email services to detect and block unwanted messages before they reach the inbox. These messages, often called spam, are usually promotional, irrelevant, or harmful. Spam filters check each email against a set of rules to decide whether to allow it into a user's inbox or move it to the spam folder.

Spam filters are essential because they protect users from scams, phishing attempts, and junk mail. Without them, email users would have to sort through hundreds of unwanted messages each week. While these filters are helpful, they are not perfect. Sometimes, legitimate emails get caught by mistake. That is why it is important for anyone who sends emails to know how spam filters work and how to avoid being flagged.

How Do Spam Filters Work?

Spam filters use a scoring system to check how likely it is that an email is spam. If an email gets a high spam score, it will be sent to the spam folder or blocked completely. The scoring system looks at many things, including:

• The email subject line
• The words and phrases used in the email body
• Whether the email contains images or attachments
• The sender's email address and domain reputation
• How many people have reported the sender as spam
• The balance of text and images
• Whether the email includes a working unsubscribe link

Each part of the email adds or subtracts points from the score. If the score crosses a certain limit, the message is marked as spam. Email services like Gmail, Yahoo, and Outlook each have their own filtering rules, but the basic idea is the same.

Why It Matters

Sending emails is one of the most common ways to connect with an audience. Whether you are sharing a newsletter, a business update, or a promotional offer, your email needs to be seen to have any value. If your messages end up in the spam folder, your audience may never read them. Worse, your sender reputation could be damaged, making future emails even harder to deliver.

That is why following email marketing best practices is important. Below are 12 ways to keep your emails away from the spam folder.

1. Use a Verified Domain

Always send emails from a domain you own, such as yourbusiness.com, instead of free services like Gmail or Yahoo. Set up email authentication using SPF, DKIM, and DMARC. These tools show email providers that your domain is verified and your emails are trustworthy. This can lower your spam score and improve deliverability.

2. Avoid Spam Trigger Words

Spam filters watch for words and phrases often used in scam or sales-heavy messages. These include terms like “act now,” “guaranteed,” and “limited time.” Instead, write naturally and clearly. Focus on helping or informing your reader. Avoid hype and overpromising.

3. Clean Your Email List Regularly

Sending emails to old or fake addresses increases your bounce rate, which hurts your sender reputation. Clean your list often by removing users who do not open your emails or who unsubscribe. You can also use an email verification tool to check if the addresses on your list are still valid.

4. Get Permission Before Sending

Only email people who have asked to hear from you. Use signup forms or checkboxes on your website. Do not buy email lists. Spam filters and email laws both look for clear permission from subscribers. If someone did not agree to receive your messages, your email is more likely to be marked as spam.

5. Write Honest Subject Lines

Your subject line should match what is inside your email. Do not trick people into opening your message by using misleading or confusing titles. Be clear and direct about the topic. Spam filters review subject lines closely, and false claims can raise your spam score.

6. Do Not Send Big Attachments

Large attachments, like videos or high-resolution images, can trigger spam filters or be blocked entirely. If you need to share a file, use a link to a secure location like your website or cloud storage. Keeping emails small and quick to load helps improve inbox delivery.

7. Use Both HTML and Plain Text Versions

Many email tools allow you to send both a rich HTML version (with design and images) and a simple plain text version of your email. Include both to make your message easier to read and more trustworthy to spam filters. Make sure both versions match in content.

8. Keep a Good Text-to-Image Balance

Emails that contain mostly images with little text may look suspicious. Some spammers try to hide text inside images. Instead, use a healthy balance of readable text and helpful visuals. Make sure your email still makes sense if images do not load.

9. Always Include an Unsubscribe Link

It should be easy for someone to stop receiving your emails. Every message must include a clear unsubscribe link, usually at the bottom. This is not just a best practice—it is a legal requirement in many places. Allowing people to leave your list helps you maintain a healthy audience and avoid spam complaints.

10. Watch Your Sender Reputation

Your sender reputation is like a score that email services use to decide if you are a good sender. It is based on how many emails you send, how many bounce, and how many people mark your messages as spam. Use tools like SenderScore to check your reputation. If it is low, stop sending for a while and focus on improving your list and content.

11. Avoid Using Too Many CAPS or Symbols

Writing in all capital letters or using lots of punctuation marks (like “BUY NOW!!!”) can make your email look unprofessional or fake. These styles are common in spam emails. Use normal formatting, sentence case, and simple punctuation. This keeps your message clean and more likely to be delivered.

12. Test Emails Before Sending

Many email platforms offer spam tests. These tools scan your email and warn you about anything that could trigger spam filters. Always test your emails before sending them to your full list. It helps you catch issues early and improve your chances of inbox delivery.