Administrator's Guide - Kerio Software Archive

Chapter 16 Antispam control of the SMTP serverThis option is not applied to checking of “email policy” records (see section 16.5) and to“black/white lists” (see section 16.2).Spam rating limitsOnce a message is tested by all enabled tests and filters, it is rated by the result spamscore. Kerio MailServer then marks the message as spam or delivers it as a legitimatemessage. The Spam rating limits scale allows set manually the limit where messages arealready marked as spam and where the spam score is so high that there is no doubt it isa spam and can be blocked:• Tag scoreIf the rating reaches or exceeds the value set, the message is marked as spam. KerioMailServer appends a special X-Spam-Flag header to the message that informs theemail client that the message is a spam.Use the entry to specify a number from 0.0 to 10.0 (the lower the number is, the morespam messages will be eliminated).We recommend you to use the 5.0 value — statistics claim that 91.12 per cent ofspam do not pass through this filter or will be marked as spam. Other 0.62 per cent oflegitimate messages, however, will also be marked as spam. If you set the score higher(i.e. to 8.0), the probability that correct messages will be blocked is lower (0.04%) andthe efficiency of spam filtering is also lower (74.36%).Warning:1. If the value you set will be too low, every message will be considered as a spam.2. If efficiency of the spam filter declines, do not lower the tag score or the blockscore. Better involve multiple tests in the spam filter.• Block scoreIf the rating reaches or exceeds the value set, the message is discarded.If the value is too low, legitimate messages might be discarded along with spam. Therefore,it is recommended to use the Forward the message to quarantine address optionwhen testing and optimizing the spam filter and specify an account where copies of allblocked messages will be delivered and stored. Copy of any message having reachedor exceeded the Block score limit will be sent to the specified mailbox. From time totime, simply scan discarded messages to check that there is no legitimate messagetrapped.Maximal block score allowed is 9.9. If the value is set to 10, the blocking is disabled,so that messages are marked as spam but never blocked.Note: If values for marking and blocking of the message are equal, all messages markedas spam are discarded automatically.If the message’s score is higher than or equal...The X-Spam-Flag header is appended to the message and the message is delivered to therecipient.In addition to marking spam messages by the special header, it is possible to prependmessage’s subject with a text which will inform user or a sieve rule that the message isa spam (such a rule can be created within creation of user accounts in the Kerio Adminis-172