When a PBX user receives a notification about a new voice message, they sees the caller’s extension name and number. The user can immediately respond to the message without having to match the phone number with its owner. This vastly improves the user experience.
For PortaSIP to use the extension’s information in the notification, enable the mailbox_use_ext_id_as_sender option on the Configuration server web interface.
If the extension information is undefined, the notification contains the caller’s phone number.