All doors lock automatically when the lock side is pressed. They unlock when the unlock side is pressed.
Driver's door

Front passenger's door

To lock all the doors from an open front door, press the lock side of the door lock switch and then close the door.
NOTE
When locking the doors this way, be careful not to leave the key inside the vehicle.
Locking, Unlocking with Transmitter
Auto Lock/Unlock FunctionMazda 6 Owners Manual: Limitations to SRS Air Bag
In severe collisions such as those described previously in "SRS Air Bag Deployment
Criteria", the applicable SRS air bag equipment will deploy. However, in some accidents,
the equipment may not deploy depending on the type of collision and its severity.
Limitations to front/near front collision ...
Mazda 6 Owners Manual: Rear door lock actuator inspection
Door Lock Actuator
1. Disconnect the front door lock actuator connector.
2. Apply battery positive voltage to the front door lock actuator terminals
and inspect the operation of the front door lock actuator.
If not as specified, replace the front door lock actuator.
With double locking ...