Here is the full list of all 23 Mail Time achievements. It takes around 1-2 hours to unlock all of the achievements on Windows.
you did it!! kinda... not really.... BUT you did do other things!
deliver meals instead of mail!
sample all the rare mushrooms!
glide for 15 minutes!
find 40 trinkets!
complete 50 deliveries!
deliver a letter in under 30 seconds!
do your part & clean up the forest!
deliver an anonymous love letter <3
deliver a fan's letter to their idol!
file an official letter of complaint >:(
find all rare coins!
complete 25 deliveries!
meet everyone in the neighbourhood!
glide for 5 minutes!
find 20 trinkets!
prevent a crime from taking place!!
complete 10 deliveries!
glide for 60 seconds!
find 5 trinkets!
take over 15 minutes to deliver a letter!
get to know your neighbourhood
Deliver your very first letter!