Does not only use an existing email list to filter - it looks at the total email, all parts to determine if it's spam. You can create a "block sender" list as well.

You can add a sender or special keywords to your friends list so that any messages that are sent from these addresses will be marked as Trusted Message by 123 Spam Filter to catch your attention, even if they contain something that would make them look like spam. This feature is also very useful if you subscribe to mailing lists. 123 Spam Filter is very quick since the entire e-mail message doesn't have to be downloaded to determine if the e-mail is junk. You can set 123 Spam Filter to check e-mail automatically in the background at a pre-determined interval. As you add and select new rules to filter out junk, 123 Spam Filter keeps a count of the number of hits a particular rule has matched. This allows you to fine-tune your selection rules.

123 Spam Filter allows you to add a sender or special keywords to your blocked senders list. Those messages sent by the blocked senders are marked as Spam.

The program will tell you in plain English why a particular message is marked as spam. A particular message will be marked if it matches any of the rules. As you build more and more rules, it can get hard to keep track of the different reasons that 123 Spam Filter suspects a message of a spam. This feature allowing you to adjust your rules if necessary.