Mail Art / Postal Art / Correspondence Art: Whatever you call it, and no matter the materials you use (be it stickers, stamps, drawings, paintings, cut and paste, or collage), it's artistic expression delivered by mail. Mail art has a wide and loyal following, you can join in and participate in group mailings and events.
This envelope was part of a class project where an envelope was mailed from one person to another, each adding their own art . . . nothing inside, just art on the outside.
If you're interested in mail art, a good place to start is Good Mail Day by Jennie Hinchcliff and Carolee Gilligan Wheeler of Letter Writers Alliance (LWA). At LWA, you'll find more information about mail art and letter writing than you can imagine—along with the curious and delightful Pigeon Post.
Mail Art is Envel-Art - Marc Swan writes contemporary poetry and mails his submissions to poetry magazines in handcrafted envelopes that he calls "envel-art." Editors, he says, respond with general appreciation and surprise. He was kind enough to share with us a few of his creations. If you're interested in Marc's poetry or envel-art, you can reach him by email.