docker-mailserver/docs/content/advanced/mail-sieve.md

User-defined sieve filters

Sieve 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.

It's even possible to install a user provided Sieve filter at startup during users setup: simply include a Sieve file in the config path for each user login that need a filter. The file name provided should be in the form <user_login>.dovecot.sieve, so for example for user1@domain.tld you should provide a Sieve file named config/user1@domain.tld.dovecot.sieve.

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.

Another example of a sieve filter that forward mails to a different address:

require ["copy"];

redirect :copy "user2@otherdomain.tld";

For more examples or a detailed description of the Sieve language have a look at the official site. Other resources are available on the internet where you can find several examples.

Manage Sieve

The Manage Sieve extension allows users to modify their Sieve script by themselves. The authentication mechanisms are the same as for the main dovecot service. ManageSieve runs on port 4190 and needs to be enabled using the ENABLE_MANAGESIEVE=1 environment variable.

(docker-compose.yml)
ports:
 - ...
 - "4190:4190"
environment:
 - ...
 - ENABLE_MANAGESIEVE=1

All user defined sieve scripts that are managed by ManageSieve are stored in the user's home folder in /var/mail/domain.com/user1/sieve. Just one sieve script might be active for a user and is sym-linked to /var/mail/domain.com/user1/.dovecot.sieve automatically.

Note: ManageSieve makes sure to not overwrite an existing .dovecot.sieve file. If a user activates a new sieve script the old one is backuped and moved to the sieve folder.

The extension is known to work with the following ManageSieve clients:

• Thunderbird with latest Sieve extension. If the extension doesn't work with the add-on available directly from within Thunderbird, try the developer build at https://github.com/thsmi/sieve.