Mail System needs Folders

I plan on keeping the mail as receipts for things I sell, over time it will get messy without some way to organize them.

What about a folder system, that way each user could sort the messages as they like.
Some people may like to sort them by Location others by goods type IE Ore, Weapons, Armor.
Also an easy way to see New or Unread or Unclaimed messages Vs old messages.

I like the Mail system but it needs to work like a more Email client.