Advantages: Can almost completely eliminate spam.
How it works: Is an email that is sent to an unknown user that has passed through the Bayesian filter but is not yet in your Allow list or Contacts. This email email asks them to confirm they are a valid user by typing in a password from the Challenge Email.
Limitations: Can increase false positives significantly. It can also cause problems with net-etiquette. It is generally not polite and can also be considered unprofessional if using this method with business email accounts. DO NOT USE this feature if you belong to newsletters or group discussions where you participate with other users. This can cause a Challenge Email to be sent to all users participating in a newsletter and this type of internet behavior is unacceptable.
Recommendations: We only recommend enabling this if the current filter methods are not effective and you do not belong to any group style participation newsletters. Please remember that not all users receiving these notices will respond even if they are good users. Also, all email receipts for goods and services you may have purchased may be blocked when using this feature.