The one-sentence version#
Content filtering evaluates message text, HTML, links, and attachments for spam patterns: deceptive phrasing, URL shorteners, image-only bodies, mismatched link text, and known malicious domains.
Why you should care#
Reputation dominates, but content still tips borderline decisions and drives the complaints that build reputation in the first place.
The mental model#
Think of spam filter content triggers as a contract between you and the mailbox providers receiving your mail. You publish or configure something they can check; they check it on every message; the result feeds their decision about where your message lands. Everything below is about making that check pass consistently.
Your first setup, step by step#
- Keep a healthy text-to-image ratio and always include a plain-text part.
- Link to your own domain; avoid shorteners and tracking domains with poor reputation.
- Make link text match the destination.
- Test rendering and spam scores before sending.
Words you will see#
- Mailbox provider: Gmail, Microsoft, Yahoo, Apple, and the corporate gateways that decide where mail lands.
- Authentication: proof that a message is from who it says it is (SPF, DKIM, DMARC).
- Reputation: the provider's running score of your domain and IP.
- Placement: whether a message reaches the inbox, spam, or is rejected.
Common mistakes#
- Image-only emails.
- Tracking links on a shared domain used by spammers.
Frequently asked questions#
Are spam trigger words still a thing?
Much less than a decade ago. Modern filters are statistical and reputation-weighted. Deceptive intent matters more than any single word.