The main features of Postfilter are

• Spam filtering at SMTP level:
  • Syntactic and DNS checkings
  • RBL/RHSBL lookups
  • local black- and whitelists
  • greylisting
  • dynamic black- and whitelists
  • can generate captcha challenges
• Individual spam filtering settings which can be managed by the users
• Personal (user) whitelists to override the spam filtering settings