TL;DR: You shouldn’t use “trigger words” like “FREE!” or “BUY NOW!!!” in your content. But even when you do, those words usually only get assigned a few fractions of a point.
Spam filters use a lot of different criteria to judge incoming email. Each factor is weighed and added up to assign a spam score, which determines if a campaign will pass through the filter. Passing scores vary depending on the server, so a campaign might pass through some filters but not others.
What Spam Filters Look For:
- Campaign Metadata
- Your IP Address
- Content and Format
Go to this list of spam assassin rules and CTRL+F for the word “FREE!” to see what we mean,
this is the current list of tests SpamAssassin performs on mail messages to determine if they’re spam or not. If you wish to change the score from the default, add a line like this to your ~/.spamassassin/user_prefs: