Kaspersky Secure Mail Gateway filters messages passing through the mail server to remove unsolicited mail (spam).
Messages are scanned for spam by the Anti-Spam engine. Anti-Spam engine scans each message for signs of spam. First, Anti-Spam engine scans the attributes of the message, such as sender and recipient addresses, size, and headers (including the From and To fields). Second, Anti-Spam engine analyzes the message content (including the Subject header) and attached files. Anti-Spam engine is enabled by default. If required, you can disable the Anti-Spam engine or disable Anti-Spam scanning for any rule. You can also limit the size of messages to be scanned for spam.
Depending on the sensitivity level, the program assigns messages in which spam or probable spam has been detected the specific statuses in accordance with the spam rating calculated by Anti-Spam.
Spam rating is a whole number from 0 to 100 that reflects the number of times Anti-Spam engine was actuated in processing the message. The program also takes into account the responses from the DNSBL and SURBL servers, results of SPF- , DKIM- and DMARC Mail Sender Authentication, and results of reputation filtering to assign a spam rating to the message.
Spam Confidence Level (hereinafter also referred to as the "SCL rating") is a spam probability assessment.
An SCL rating can take the following values:
Based on the scan results, the program adds the X-MS-Exchange-Organization-SCL X-header containing the SCL rating to the message.
Reputation filtering is a cloud service that uses a technology that determines the reputation of messages. Information about new kinds of spam appears in the cloud service sooner than in Anti-Spam module databases, making it possible to improve the speed and accuracy of spam detection.
Depending on the status assigned, the program performs actions in accordance with the message processing rule settings. You can select actions to be performed by the program on messages with a certain status and configure tags to be added to messages based on the Anti-Spam scanning result. The default action performed on messages is Skip.