Here is the full list of all 20 KeyWe achievements.
The base game contains 16 achievements, and there is 1 DLC pack containing 4 achievements.
Earn Postmaster on all Winter levels
Earn Postmaster on every level in the Calendar
Earn Postmaster on all Autumn levels
Earn Postmaster on all Summer Levels
Find every Collectible
Complete every level in Winter
Beat your previous score on a level
Complete every level in Autumn
Find a Collectible
Complete an Overtime Shift for Bonus Pay
Complete every level in Summer
Complete the first week of Summer
Become registered Teleposters.
Earn Postmaster on every Overtime Shift
Earn half of the wearables in the Wardrobe
Earn all of the wearables in the Wardrobe