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: Schedule 1
U.S.A. and Puerto Rico residents - Engine oil flexible maintenance interval
Use when the maintenance monitor for “Oil Change” is set to “Flexible”. For
details, see maintenance monitor.
Chart symbols:
I: Inspect: Inspect and clean, repair, adjust, fill up, or replace if necessary.
T: ...