Did you just LOVE getting mail as a kid? I know I did, so I took my own spin on sending and receiving mail, for Skylee's Quiet Book. Here she can keep a pen and some paper handy, write a note and send it off, OR get a little note from Mommy!
The envelope is open at the top where little pieces of paper are stored, and a place to hold a pen or pencil. Simple and functional :)