The Mailman is always seen wearing his blue mailman uniform. He has a mustache and is usually (almost always) wearing his mailbag slung around one shoulder.
The Mailman first appeared in the episode Special Delivery when delivering Walden's package to Wubbzy. And He Had A Important Role In Broken Record, Which Appears To Be Chased By A Buzzlebug. The last episode the Mailman appeared in was Run for Fun, where he ran in the Wacky Dash while still carrying his mailbag.