How to avoid content filters

This article applies to:

You’ve crafted the perfect email for your next marketing campaign... complete with an attention grabbing subject line, compelling copy, and an irresistible call-to-action. Your positive click rates will be through the roof! Unfortunately, your email campaign winds up filtered as spam, sent to the junk folders, or dropped by the Internet Service Provider. You may have been stopped by a content (or spam) filter!

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What is a content filter?

Internet service providers use a series of filters to identify spam before it ever hits your inbox. Providers like Gmail scan and filter emails from users that are deemed to be objectionable or harmful. These emails may wind up rejected by the ISP servers or put in a junk folder. The ISPs follow users’ behaviors and continuously improve the filtering logic over time. For example, if Gmail notices a user never engages with certain emails or if the emails are marked as spam, Gmail will proactively send future emails from that company to the junk folder. 

Although providers keep their filtering algorithms pretty secretive, there are some best practices we can share to assist you as you construct your emails.  

You can use mail-tester to test and grade your your email and receive suggestions before launching campaigns.

High risk industry

Some industries’ email content result in higher-than-average spam complaints, which negatively affects deliverability for the rest of our customers. To mitigate this risk, Keap does not contract with these industries.

Sender domain health

Your domain health plays a large role in your overall email reputation, which can factor into your inbox placement. Your email reputation, similar to your credit score, is created by your email marketing practices. This is similar in concept to how your credit score is determined by your financial practices. Prior to purchasing a house or car, you would check your credit score to ensure you’re in good standing. The same is true for launching an email campaign. Check your domain health first using the following steps:

  1. Go to
  2. Click blacklists.
  3. Enter your business domain.
  4. If you find yourself on a blacklist, follow the de-listing instructions on the blacklist site prior to sending your email.  

Link health

Did you know the links included in the body of your email are checked as well? While you’re checking your domain health in MxToolbox (above), check all the links in the email as well.

Keywords in subject lines and body

Over time, the email industry has compiled a list of key words that trigger spam complaints more often than others.  Even if you use one of these words in a legitimate email that your recipients expect and want, it can still contribute to the possibility that your email will be marked as spam.

Examples of Spammy Words:

  • $$$
  • Cash
  • Certain keywords can trigger spam filters such as:
  • Free
  • Free money/ offer/ quote
  • Great offer
  • Stock pic
  • Instant Access

Check out The Most Common Spam Words (updated for 2021)

Unsubscribe link

Make it easy for people to unsubscribe! Don’t attempt to hide the unsubscribe link by adding extra spacing. If your recipients cannot find the opt-out link they will resort to reporting the email as spam. This can contribute to complaint rates that can damage your email reputation.


Some filters can be triggered based on the formatting or images within the email. A couple recommendations:

  • Maintain a text to image ratio of 80:20.
  • Be consistent with branding, content, and formatting so customers are familiar with your emails and will expect it.
  • Refrain from using short URLs, which is often associated with spam.

Following these tips does not guarantee that your emails will always land in the inbox and never be flagged by a content filter. Ultimately, the best way to stay away from spam filters is to A/B Test, and spam test everything!

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