Лицензия исходного кода

GNU Affero General Public License (AGPLv3)

The extension is free and open source software, it is made available to you under the terms of the  GNU Affero General Public License (AGPLv3). This means you may use, copy and distribute it to others. You are also welcome to modify the source code as you want to meet your needs.

See http://sieve.mozdev.org for more details