If you'd like to practice the lost art of writing letters, you can also practice the 3Rs.
Save envelopes you get in the mail or happen to have around you, and use them again for mailing things out.
This is the photo at the Post Office of the reused envelope I used to send a gift to a friend. After it left the Post Office, the friend on the other end got it with no trouble. And it makes the mail all the more interesting!