A toner cartridge according to one example embodiment includes a housing that defines a reservoir for containing toner. An exit port in fluid communication with the reservoir faces downward on the front of the housing near a first side. A shutter positioned at the exit port is movable between an open position and a closed position. A toner delivery system for transferring toner from the reservoir includes a main interface gear exposed on the front of the housing near the top of the second side. A rearward facing opening is positioned near the first side of the housing for receiving a first engagement feature in an image forming device for opening and closing the shutter. A forward facing slot is positioned near the first side of the housing for receiving a second engagement feature in the image forming device for locking and unlocking the shutter.