There is no requirement that you attempt to effect delivery to the intended recipient. The legal obligation would be met by writing “not at this address” on the

There is no requirement that you attempt to effect delivery to the intended recipient. The legal obligation would be met by writing “not at this address” on the envelope and putting it back in the mailbox. I imagine if you tried to abuse this and then sue your case would be thrown out of court. It would also be awfully expensive; compare the cost of postage to send all those letters with the cost of a rubber stamp to have them returned.