You can set R-Key Setting.
For information on the optional products required to use this function, see "Optional Products Required for Each Function."
1.
Press 
→ [Function Settings] → [Send] → [Fax Settings] → [R-Key Setting].
→ [Function Settings] → [Send] → [Fax Settings] → [R-Key Setting].2.
Select [PSTN] or [PBX].