Chapter 13 Antispam control of the SMTP server
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## Chapter 13 Antispam control of the SMTP server

Antispam control of SMTP server protects users from spam. Spam is an unwanted, usually advertisement email. Spam are usually sent in bulk and the recipient addresses are obtained by illegal means (e.g. by tapping the network communication).

Kerio MailServer includes many options and features to dispose of spam. These features include various filters, testing and monitoring technologies which help distinguish quite precisely spam 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 13.4 SpamAssassin).

- Black/White lists (detailed information on their features and settings, see section 13.2 Blacklists tab).

- Proprietary filtering rules (detailed information on their features and settings, see section 13.3 Custom Rules).

- Caller ID (detailed information on its features and settings, see section 13.5 Email policy records check).

- SPF (detailed information on its features and settings, see section 13.5 Email policy records check).

- Delayed response to SMTP greeting (detailed information on their features and settings, see section 13.6 Spam repellent).

Each test can be used separately or combined with the others. To achieve better efficiency, it is 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. Also the spam detection will be more successful which will reduce number of messages marked as spam by mistake (so called “false positives”).

Each testing type uses specific methods to detect spam. There is, however, a feature most of the 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 of such messages. The other is to raise the so called spam score (for details, see chapter 13.1 Spam Rating tab). Messages with a score too high awarded by multiple tests are discarded (individual scores are summed). The first alternative may help reduce load on the server, the second one eliminates better possible “false positives”.

### Warning

When Kerio MailServer is connected offline, efficiency of the antispam filter decreases dramatically.

To set Kerio MailServer's spam filter, go to Configuration → Content Filter → Spam Filter.

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12.6 Advanced Options | Contents | 13.1 Spam Rating tab