I have a 3CX in my office behind a router/firewall/NAT. And I'm trying to use an analog phone at my home with a FXS ATA device (Grandstream HandyTone 286). The extension I'm using is marked as "Extension is external" in 3CX. When incoming calls arrive (calls from 3CX to the ATA device), the Via header of the INVITE message has the internal IP address instead of the public (STUN resolved) IP address. The ATA device is trying to send responses to the internal IP address, so responses never arrive to 3CX. Is there any way to make 3CX use the public IP address in the Via header, when the extension is external? Thanks in advance.