I have found so many great ideas online for how to set up a desk area for children to have a mail center. Playful Learning has some great ideas, but they all take up quite a bit of space. This mama does not have that much room in her house to devote to a writing center. So alas, I came up with my own mini-version.
A 3-ring binder.
We send a lot of mail to daddy. When he was at basic, we sent mail every day. This binder has everything we need to send a letter to him. I have several different pocket/sleeve protectors, so we use baseball sized ones for addresses, and larger pockets for some blank cards, and I also have a pouch for her stamp and a few markers/pens. She also has full access to other pens/markers/crayons if she so desires.
The front of the binder has various stickers (I separate the letters from just generic stickers). The back is where all the paper is. I try to keep a variety of lined (college rule, and learning to write lined/dotted paper, as well as fancy paper/stationary and colored paper).
The binder is kept on a low shelf easily accessible to O, so she can use it anytime she pleases, but it can also be tucked away when it is time to work on something else.