From the control panel, navigate to:
Settings > Fax > Analog Fax Setup > Fax Receive Settings > Holding Faxes
For non-touch-screen printer models, press to navigate through the settings.
Select a mode.
Block unknown numbers to stop receiving unwanted fax messages.
If you experience failure in getting incoming faxes, then make sure that the trays and the toner cartridge are not empty.