How NoSpamProxy Protection classifies emails as spam

In the rules you configure various filters and actions. Filters evaluate emails and thereby influence the Spam Confidence Level (SCL) of the emails. The SCL determines whether the email is rejected if the inspection result exceeds a certain SCL. See Rules, .Filters in NoSpamProxy and Actions in NoSpamProxy.

  • The higher the SCL, the higher the probability that the email is spam.
  • The lower the SCL, the lower the probability that the email is spam.
  • An SCL of 0 indicates that the email has been classified as neutral.
  • The value range for the SCL extends from -10 and +10 points.

You can weight the filters differently within the rules using the multiplier. The weighting of the filter is calculated with the multiplier. This allows you to influence the influence of the individual filters within a rule. If this total weighting reaches the threshold value of the rule, the email is treated as spam and rejected.

TIP: The modular structure of the rules offers numerous possibilities for individual adaptation. In addition, the filter weighting with multipliers is crucial. For details on how the SCL is calculated, see Spam Confidence Level (SCL).


You have created a rule with one active filter: the word filter. Also, Level of Trust is enabled for this rule. The word filter checks an email for unwanted expressions. Let us assume that an email contains a large number of unwanted expressions. The word filter will therefore sound the alarm on this email and deliver a high penalty value, for example 6. If the word filter were the only filter in this rule, the email would now have a total value of 6. For example, if you usually set the threshold value to 4, the email would now be blocked and rejected. The sender would receive an non-delivery report.

Keep in mind that Level of Trust is still activated in this rule. The email comes from a very reliable email partner with whom you have exchanged many emails. Level of Trust assigns -4 SCL points to this email.

The Level of Trust system always has a multiplier; this multiplier is composed of

  • the sum of the multipliers of all filters activated on the rule and
  • the value 1, which is added to this sum.

This reults in a factor of 2 in our example. The SCL value is therefore 6+2*-4. This results in an SCL of -2. The email would pass through NoSpamProxy Protection.