How long is mail held when not delivered in the United States?

I had heard they hold it for about 6 to 8 days if they haven't heard form you via forwarding or hold request before returning to sender. That, of course, assumes you have a small box and receive letters frequently (which I do because I owe so many entities money).

On the other hand, I once went to the post office two weeks (13 days actually) after not receiving any mail at all and to my surprise they said "so you're Mr. Calmorte!" in a friendly but also kind of pissed off at being disrespected as a public employee kind of way.

I also had the mail carrier say "you don't even need to tell anyone but me" about an address change when I changed addresses within a building (long story, trust me). But then I wasn't getting any mail for awhile. That's when I went to the distribution center and they said "so you're Mr. Calmorte!" and handed me like 50 envelopes from parking tickets, the IRS, and some jagoff education financial company in Tennessee.

It all depends on your mail carrier, the local post office, how often you receive mail, and how important and unique the letters look. If you live in a condo, have lazy or stupid carrier, and your mailbox fills up with credit card offers and local coupon books every four days, you're in trouble. You're probably in trouble in a lot of ways, but one of them is definitely returned mail.