The SMTP server is accessible from the Internet and, therefore, it is necessary to configure an antispam control of the SMTP server. Antispam filters can be set under :
Antispam rating can be started and set on the Spam Rating tab. Default settings of this tab can be kept.
On the Blacklists tab, it is recommended to enable control involving Internet spammer databases and to set 2 points as a score for each database.
Switch to the SpamAssassin tab and enable option Check every incoming message in Spam URI Realtime Blocklist (SURBL) database.
On tabs Caller ID and SPF, set control of e-mail policy records of the sender SMTP server and set the spam score to 2 points. This control allows to filter out messages with fake sender addresses.
On the Spammer Repellent tab, enable SMTP connection delay. This filter efficiently stops spam messages at the SMTP level which relieves the server from a remarkable volume of spam testing.
Antispam filters of the SMTP server are focused in the Kerio MailServer, Administrator's Guide, chapter Antispam control of the SMTP server.