Created Configuring Sieve filters (markdown)

docs/content/advanced/mail-sieve.md

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+### User-defined sieve filters
+
+[Sieve](http://sieve.info/) allows to specify filtering rules for incoming emails that allow for example sorting mails into different folders depending on the title of an email.
+
+To specify a user-defined Sieve filter place a `.dovecot.sieve` file into a virtual user's mail folder e.g. `/var/mail/domain.com/user1/.dovecot.sieve`. If this file exists dovecot will apply the filtering rules.
+
+An example of a sieve filter that moves mails to a folder `INBOX/spam` depending on the sender address:
+
+```
+require ["fileinto", "reject"];
+
+if address :contains ["From"] "spam@spam.com" {
+   fileinto "INBOX.spam";
+} else {
+     keep;
+}
+```
+
+***Note:*** that folders have to exist beforehand if sieve should move them.
+
+For more examples or a detailed description of the Sieve language have a look at [the official site](http://sieve.info/examplescripts).