Administrator's Guide - Kerio Software Archive

Chapter 16Antispam control of the SMTP serverAntispam control of SMTP server protects users from spam. Spam is an unwanted, usuallyadvertisement email. Spam are usually sent in bulk and the recipient addresses are obtainedby illegal means (e.g. by tapping the network communication).Kerio MailServer includes many options and features to dispose of spam. These featuresinclude various filters, testing and monitoring technologies which help distinguish quite preciselyspam messages from desirable email.To detect and eliminate spam, Kerio MailServer uses the following methods and tests:• SpamAssassin (detailed information on its features and settings, see section 16.4).• Black/White lists (detailed information on their features and settings, see section 16.2).• Proprietary filtering rules (detailed information on their features and settings, see section16.3).• Caller ID (detailed information on its features and settings, see section 16.5).• SPF (detailed information on its features and settings, see section 16.5).• Delayed response to SMTP greeting (detailed information on their features and settings, seesection 16.6).Each test can be used separately or combined with the others. To achieve better efficiency, itis recommended to combine as many antispam features as possible. The more tests are used,the denser is the antispam filter and the less spam will be delivered to user’s mailbox. Alsothe spam detection will be more successful which will reduce number of messages marked asspam by mistake (so called “false positives”).Each testing type uses specific methods to detect spam. There is, however, a feature most ofthe tests have in common. For all methods except the Delayed response to SMTP greeting,two actions can be set of what how spam messages would be handled. One action is denial ofsuch messages. The other is to raise the so called spam score (for details, see chapter 16.1).Messages with a score too high awarded by multiple tests are discarded (individual scores aresummed). The first alternative may help reduce load on the server, the second one eliminatesbetter possible “false positives”.Warning: When Kerio MailServer is connected offline, efficiency of the antispam filter decreasesdramatically.To set Kerio MailServer’s spam filter, go to Configuration → Content Filter → Spam Filter.170