Why are IP adresses instead of calling numbers shown in the header of fax or voicemails?

An incoming fax or voicemail in the user's inbox shows an IP adress instead of the callnumber of the sending person in the header.

Open the XCAPI configuration (expert mode: View -> expert mode) and navigate to the set controller -> Callnumberfilter settings -> tab "Callnumber from Network".

Trough deleting of the complete entry "IP V4 (separation marks)" the transfer of the IP address won't happen again.