So mail is a pretty good system but there are A LOT of flaws here are my fixes to them.
First fix: When I do /mail read I often read starting from the top down and am very confused about what the person is saying until I remember we are supposed to go down to up. idk if this is just me, but if it ins't fix it so the mail is in order of up to down
Second fix: Often when I go to read my mail I want to know when the person was online or how long ago I got this mail etc. It's pretty small but just add like a little time stamp at the end of mail.
Third fix: Make it so you can delete a certain piece of mail or by a sent by a certain person. Often I have important coordinates or a time in my mail, but then I also have like 7 other things that I don't need anymore. Make it so instead of just deleting all of them that you can choose which one to delete.