Administrator's Guide - Kerio Software Archive

16.3 Custom RulesUse the Add button (or Edit) to open a dialog where rules can be defined or modified.Figure 16.6Defining ruleFiltering rules consist of the following items:DescriptionComment on the rule (for use of administrator).HeaderTested part of email message header. You can choose from various predefined options(From, To, Cc, Subject and Sender) or create a custom one (i.e. X-Mailer). Do not usecolons while defining header names.The From and To items slightly differ from the other ones. These items are checked forthe From and To headers in email and for headers included in SMTP envelopes. The Fromitem is compared with MAIL FROM: and the To item is compared with RCPT TO:. Anyother items are compared with headers included in the email itself only.This implies the following facts:Any other settings for blocked messages do not apply to messages rejected on SMTPlevel. Any message meeting the denial rule is rejected and marked with the standard 553error code (this code means that it is a persistent error and the SMTP server will not retryto deliver it) and a DNS message is sent to the sender.To rules regarding From and To items, a special exception regarding their order in therule list is applied (see above). If the From and To rules are starting the rule list (no otherrule precedes them), they are executed against the MAIL FROM: and RCPT TO: headerson SMTP level. If there is even a single rule preceding these rules which is tested againsta different header, the message is automatically accepted in the queue of incoming mes-179