Why It Matters
Filters are the gatekeepers between your send button and your recipient's eyeballs. Even with perfect content and a clean list, if filters flag your emails, they vanish into spam. Understanding how filters work gives you a real edge — you can structure your emails to avoid common triggers and consistently reach the inbox.
How It Works
Modern spam filters are far more sophisticated than the keyword scanners of the early 2000s. They use machine learning models that weigh hundreds of signals: sender reputation, authentication results (SPF, DKIM, DMARC), content analysis, link reputation, sending patterns, and — critically — how past recipients interacted with your emails. Gmail's filters, for instance, heavily weigh individual recipient engagement. An email one person sees in their inbox might land in spam for someone who never opens your messages.
Quick Tips
- Don't obsess over avoiding "spam words" — modern filters care far more about your sender reputation and authentication than whether you wrote "FREE" in caps
- Keep your text-to-image ratio reasonable; emails that are just one big image with minimal text look suspicious to filters
- Avoid URL shorteners (like bit.ly) in emails — spammers abuse them heavily, so filters treat them with suspicion