From the United States Postal Service:
First-Class Mail® and Priority Mail®
First-Class Mail and Priority Mail service is forwarded for 12 months, at no charge, as long as the sender did not place a non-forwarding endorsement on the mailpiece
During months 13-18, the mail is returned to sender with the new address
After 18 months, the mail is simply returned to the sender
Express Mail®
When forwarded, Express Mail service receives the same expedited treatment as before; however, the delivery guarantee is void
Express Mail is forwarded for 12 months as long as the sender did not place a non-forwarding endorsement on the mailpiece
During months 13-18, the mail is returned to sender with the new address
Periodicals
Magazines and newspapers are forwarded for 60 days, at no charge
After 60 days, the Computerized Forwarding System (CFS) will handle the periodical based on the type of COA the customer has on file:
Temporary COA - Periodicals will be disposed of
Permanent COA - Periodicals are returned to sender with the new address
Accountable mail
Accountable mail can be forwarded when a COA is on file, but the delivery guarantee is voided for these mail pieces
Standard Mail®
Standard Mail, such as mail-order merchandise under 1 pound, circulars, and catalogs are forwarded only with special endorsements from the mailer
Package Services and Commercial Parcel Select
Package Service Mail (includes Parcel Post, Library Mail, Bound Printed Matter, Media Mail), with no endorsement, is forwarded locally for 12 months at no charge. Additional forwarding charges are paid by you if you move outside the local area (includes packages weighing 16 ounces or more not mailed as Priority Mail service).
International Mail
Express Mail service, Periodicals, Package Services, and Standard Mail items are not forwarded internationally. In addition, First-Class Mail and Priority Mail service items that contain a non-forwarding endorsement or appear to contain merchandise are not forwarded internationally.
First-Class Mail, Priority Mail cards, and unregistered letters are forwarded internationally, for 12 months, as long as both of the following conditions are met:
The mailpiece does not contain a non-forwarding endorsement
The mailpiece does not appear to contain merchandise
A temporary COA forwards mail for 6 month intervals, not to exceed 1 year
The Post Office™ will advise publishers of a customer’s new address
All international mail that is not forwarded will be treated as RTS (returned to sender) or waste, depending on the class of mail