Storage for Penpal Correspondence

How do you store your penpal letters?  If you don't have a penpal, then maybe I'm asking you how do you store things like birthday cards or any other correspondence? I was storing my stuff in a box, then it moved to a plastic band then basically it just moved to the floor and yep, it was a mess so I decided to do something about it.

Some things that I've been doing

It's April, when did that happen? How did that happen? I struggle to know what day it is, let alone the month! Yesterday we were in our shorts & tshirts and at the beach, today I've got my cardigan on & raincoat at hand! 

So, what have I been doing? What have you been doing?
I've been making some envelopes,