Spam triggers
📖 3 min readUpdated 2026-04-19
Spam filters look for patterns in content, structure, and sending behavior. Avoiding triggers improves inbox placement.
Content triggers
- ALL CAPS
- Excessive exclamation!!!
- Words: FREE, ACT NOW, GUARANTEED
- Too many links
- Large images with little text
Structure triggers
- Image-only email
- Shortened URLs
- Weird formatting
- Missing plain-text version
Sending triggers
- Volume spikes
- Sending too fast to unengaged
- Purchased lists
Test before sending
Send to Mail-tester.com, get score. Aim for 9+/10.
What to do with this
- Avoid classic spam phrases especially in subject lines, "free", "guarantee", "act now", "limited time" all trip filters
- Keep image-to-text ratio balanced, image-only emails pattern-match to phishing and hit filters
- Never attach files to marketing email, attachments trigger virus scans and signal non-legitimate sending
- Use your own tracked domain for links instead of bit.ly, URL shorteners on mass sends look suspicious to filters
- Pre-check every campaign at mail-tester.com, 9+/10 score before sending is the minimum bar