You need to make the following settings to send and receive IP faxes to and from a G3 fax-compatible device through a VoIP Gateway.
Setting SIP information for the printer
Register a VoIP gateway
To use VoIP gateways, you need to set the priority for the VoIP gateways you want to connect to after they have been registered. See the following for more information.
Access Web Config, and then select Fax tab > IP-FAX Settings > VoIP Gateway Settings.
Set each item.
Click OK.
The settings are reflected on the printer.