When you turn in a post office change of address, you are instructing the post office to forward certain mail addressed in your name to your old address to your new address. The post office will forward First Class, Priority mail, and Express Mail for one year from the start date you indicate on the form. They will stop delivering mail in your name to your old address on the start date. It may take 7 to 10 Postal business days to begin receiving this forwarded mail at your new address.
The Postal Service will forward Periodicals for 60 days. This would include things like newspapers, journals, and magazines. Standard Mail such as most catalogs, coupons, flyers, and other advertising mail is not forwarded without special instructions from the sender. Non-profit Org. mail is also not forwarded. So if you want to continue receiving mailings from a non profit organization such as a church, synagogue, or charity, be sure to notify them of your new address.
After the forwarding time expires, the post office will return mail that is still addressed to your old address to the sender. They will include a sticker on the mailpiece notifying the sender of your new address. This will happen for an additional 6 months. After 18 months, the change of address request expires and the information is no longer kept on file. Mail that still is being sent to your old address at that time will be returned to the sender as "Unable to Forward" or "Attempted Not Known".