A few years ago, for a period of about 6 months, I was having half my mail marked as "Return to sender - no such address"
No - I had not requested the mail to be forwarded or any other service - just random pieces of normal mail coming in was being marked "Return to sender - no such address" Worst part was - some of the mail was from the IRS.
Curious how the post office could not suddenly find mail mailbox - given it is a PO box in the the post office. Had it for several years. Still have it.
I avoid using the US Snail service if at all possible.