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!
glide for 15 minutes!
find 40 trinkets!
sample all the rare mushrooms!
complete 50 deliveries!
glide for 5 minutes!
prevent a crime from taking place!!
meet everyone in the neighbourhood!
deliver an anonymous love letter <3
deliver a fan's letter to their idol!
complete 25 deliveries!
find 20 trinkets!
take over 15 minutes to deliver a letter!
do your part & clean up the forest!
deliver a letter in under 30 seconds!
glide for 60 seconds!
complete 10 deliveries!
file an official letter of complaint >:(
find all rare coins!
find 5 trinkets!
get to know your neighbourhood
Deliver your very first letter!