Here is the full list of all 31 Mail Mole achievements.
Win all the races against Mecha Moles
Purchase all outfits
Save Carrotland's Summer Festival
Recover all the power cells of the second tower
Complete Spooky Swamp
Find all the radishes
Purchase 20 outfits
Complete Magma Rocks
Recover all the power cells of the first tower
Complete Yeti Ridge
Beat Pukat's fourth machine
Complete Dry Canyon
Beat Pukat's third machine
Expand your world
Complete Coconut Island
Complete Ancient Temple
Beat Pukat's second machine
Save 1000 carrots
Save 500 carrots
Get a gold medal
Win a race against Mecha Moles
Meet Scarlett the Skunk
Complete Carrot Fields
Save 300 carrots
Beat Pukat's first machine
Purchase an outfit
Reopen Rick's Store
Finish the tutorial
Recover all power cells, win all races, get all medals, buy all the clothes
Get 15 gold medals
Get all gold medals