If the IP line is used in the local machine or the remote machine, switch the setting values for fax sending/receiving to those suitable for the IP line to improve the communication quality.
Select [Fax Settings] - [Function Setting] - [Recommended settings for IP line] in administrator mode of Web Connection (or in [Utility] - [Administrator] of this machine), and configure the settings. For details, refer to [Recommended settings for IP line].