This article covers how email content filters work, why emails get filtered to spam, and best practices for improving email deliverability when sending through Keap™.
What Is a Content Filter?
Content filters are used by inbox providers such as Gmail, Outlook, and Yahoo to screen incoming messages for signs of spam, phishing, or other abusive behavior before they reach a recipient's inbox. Filters evaluate:
Subject lines and body content
Engagement history
Sender reputation and domain health
Link reputation
Formatting and structure
If an email fails these checks, it may be sent to the junk folder, bounced, or blocked — even if the recipient expects to receive it.
Why Emails Get Filtered
Inbox providers continuously refine filtering logic based on user behavior. If recipients ignore, delete, or mark emails as spam, future emails from the same domain are more likely to be filtered — including for recipients who actively want them.
Best Practices to Avoid Content Filters
Avoid High-Risk Industry Content
Certain industries — such as affiliate marketing, adult services, payday loans, and cryptocurrency — have high spam complaint rates. Keap does not support email sending for industries listed in the Acceptable Use Policy to protect platform-wide deliverability.
Monitor Domain Health
Domain reputation affects whether emails are delivered. Poor sending practices lower domain reputation and increase the likelihood of filtering. To check whether a domain is blacklisted:
Navigate to hetrixtools.com.
Select Blacklist Monitor.
Enter the domain name and run the check.
If the domain appears on a blacklist, follow the de-listing instructions provided before sending any further emails.
Check Link Health
All links in an email — including legitimate ones — are scanned by content filters. Links to suspicious or blacklisted destinations increase filtering risk. Best practices for links:
Avoid shortened URLs such as bit.ly or tinyurl.
Use full, branded URLs.
Ensure all links resolve correctly and lead to secure HTTPS pages.
Run link health checks at hetrixtools.com.
Avoid Spam Trigger Words
Certain keywords are frequently associated with spam and can increase filtering risk even in legitimate emails. Common examples include:
Free / Free money / Free quote
Cash / $$$
Instant access
Great offer
Risk-free / No obligation
Stock pics
For a more complete reference, see the Glock Apps Email Spam Words guide.
Make the Unsubscribe Link Easy to Find
Hiding or obscuring the opt-out link causes recipients to mark messages as spam instead of unsubscribing. Best practices:
Place the unsubscribe link clearly in the email footer.
Use standard font size and spacing.
Honor unsubscribe requests promptly.
Optimize Email Formatting
Poor formatting signals to filters that an email may be spam. Best practices:
Maintain a text-to-image ratio of approximately 80:20.
Avoid sending image-only emails.
Avoid excessive formatting such as ALL CAPS, bright red text, and oversized fonts.
Use consistent branding and structure across emails.
Test Before Sending
Testing an email before sending reveals how it may be scored by spam filters. Recommended tool:
mail-tester.com — Scores the email and provides specific recommendations for improvement.
Deliverability Checklist
Monitor domain and link health regularly.
Avoid high-risk content and spam trigger words.
Keep email formatting clean and balanced.
Place the unsubscribe link prominently in the footer.
Test every email campaign before sending.
Following these practices reduces the risk of content-based filtering. Inbox placement cannot be guaranteed by any sender, but consistent adherence to these practices significantly improves deliverability outcomes.
Recommended External Resources
The following third-party services provide professional guidance and tools for improving email deliverability:
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Email deliverability consulting and software
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List cleaning
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Form security
Frequently Asked Questions
What does this article cover?
This article covers how email content filters work, why emails are filtered to spam, and best practices to improve email deliverability in Keap.
Can inbox placement be guaranteed?
No. Inbox placement depends on a combination of factors including sender reputation, content quality, recipient engagement, and inbox provider filtering algorithms. Following deliverability best practices significantly reduces filtering risk but cannot guarantee delivery to the inbox.
Does Keap support all types of email sending?
No. Keap does not support email sending for certain high-risk industries. See the Keap Acceptable Use Policy for the full list of restricted use cases.
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