What Spam Filters Look At
Stop words aren't the only thing that spam filters analyze. They also look at:
- Domain reputation and IP — how long ago the domain was registered, whether there is a website on it, how many emails were sent, whether subscribers complained about spam.
- Authentication settings: whether the domain has SPF and DKIM.
- DMARC is a technology that tells you what to do with an email that fails SPF and DKIM verification.
- Individual settings of spam filters — users can choose who to receive mail from and who to send to spam.
- The content of the email — whether the text and HTML versions of the email are the same, whether the links work, how often the fonts change, and whether there are any forbidden elements in the template (JavaScript, Flash). Messages with frequent font changes, colorful inserts, Caps Lock, and millions of exclamation points are often sent to spam. The algorithm also evaluates the text of the email, layout, and design features.
Stop words refer to the last point — the content of emails.