Multi-path call forwarding is used to signal internal and external calls, in addition to call distribution for an internal or an external number, e.g., on a smartphone. Multi-path call forwarding is also executed if the "main phone number" is, for example, busy.
For call forwarding to an external number: The external destination must be reachable for the user. For this, the exchange line routing settings (with block- and allowlists) that apply for the user/group are proved before a multi-path call is executed.