Reference

The VoIP process flow is rather complicated, but from the priority point of view we can simplify it and describe an incoming call in these routing phases:

1. The dial plan is processed first.
2. VoIP trunks next.
3. Location service next (registered VoIP users).
4. Extensions.

If you have your extension linked to an email account or a list of members and there are no preceding rules for the number, the extension will route the call accordingly.

So not only you can define the available extensions and groups in your system but you can also control to whom they are linked to automatically.