Keep in mind, Sieve is a powerful mail filter, loss of data is likely when you misconfigure a script. Furthermore is likely that this extension contains bugs. As the source code is freely available, every one can check the correctness and the quality of the software before using it. This means you use the extension at your own risk. There is absolutely no liability for loss of data or damage or similar stuff caused by this extension.
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.
All of the source code is available under licenses which are both free and open source. Most of it is available under the AGPLv3. The remainder of the software which is not under the AGPLv3 is available under one of a variety of other licenses. Those are given below:
- CodeMirror is released under a MIT Style license
- JQuery is released under the MIT License
If you don't agree with any of these licenses, don't use the extension! As every country has it's own jurisdiction, it could be that parts of the license or the whole license itself is illegal, invalid or violates a law of your country. If so you are not allowed to use the extension!