So lately I know I haven't gotten some mail I was expecting, so I mailed a letter to myself from the next city over with a good return address (not mine). Well, I never got this 'test letter', but then 8 days later it shows up at the return address with a yellow sticker on the envelope that said: Return To Sender Not Deliverable as Addressed Unable to Forward I used an envelope with a see through window and purposely made the print-out of my address very clear and easy to read. The address is 100% correct. So does anyone know how mail is sorted at the Post Office? Is this the result of a machine sorting problem? Anyone here work or have worked at a Post Office that could tell me what possibly happened? Any ideas/suggestions would be helpful. Obviously I need to talk to the Post Office, and this is probably why I haven't gotten other mail lately.