DNSBL

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DNSBL (Domain Name Server Blackhole Lists) or RBL (Realtime Blackhole List) services are quite effective against spam. Every service contains a list of black server IP addresses that are used to send spam. These services are accessed in real time using the DNS protocol.
To evaluate a message, the plug-in makes a query to the list of the selected DNSBL services with the sender's IP address. If the IP address is listed in several black lists (the number of required hits can be changed in the settings), the message is marked as spam.

You can select several services from the list in the DNSBL dialog box. Set the minimum number of required hits less than or equal to the number of the selected services.

It is possible to estimate the effectiveness of DNSBL services using the counted statistics:
- Number of hits is the overall number of IP addresses found in the corresponding DNSBL.
- Number of false positives is incremented each time when you mark as non-spam a message with sender IP from the corresponding DNSBL.