Roy doesn't use stamps on his mail. He just drops his letters in the mailbox with no postage. Instead of stamping them "RETURNED: POSTAGE DUE" the USPS stamps them, "HAPPY TO SERVE YOU MR. HOBBS, IS THERE ANYTHING ELSE WE CAN DO FOR YOU TODAY." (of course he never sees this because the mail gets delivered elsewhere, but a few of the mail recipients have informed him about it, so you know it's true...and, um...yeh...)