Developed by Apache Software Foundation, SpamAssassin a Pearl-based email spam-filtering computer program, which can be used as an independent spam filtering application or a subordinate program to other spam filtering programs.
There are two ways to work with SpamAssassin:
- Integrate the program into the mail server so it will fulfill the automatic filtering of mail sent to the website.
- Integrate with several mail clients to be run by individual users.
Spam-filtering methods of SpamAssassin:
- DNS-based blackhole lists and DNS-based whitelists
- Fuzzy-checksum-based spam detection filters
- Hashcash email stamps based on proof-of-work
- Sender Policy Framework and Domain Keys Identified Mail
- URI blacklists which are tracking spam websites
SpamAssassin applies a variety of rules that are used to detect whether mail is spam or not. In the program's documentation, these rules are called "tests." Each test has a certain value, which will be assigned to a message if it matches the criteria. The value can be negative or positive. A positive value means that the message is "spam" and a negative value stands for non-spam.
By combining all the test scores, the program compiles a general score. SpamAssassin sets the score threshold, which defines whether the message is spam or not. Usually, a message has to match multiple tests in order to be classified as spam. One only test match will not mark it as spam.
SpamAssassin is free software, also called open source.