Mail forwarding is a service offered by the post office (or other mailing companies) that allows you to have all your mail sent to a different address. For example, if you move to a different house or you are traveling, you can have all your mail sent to a different address so that you can still get it. When you sign up for mail forwarding, you give the post office (or mailing company) the address where your mail should be sent, and then all the mail meant for you will be sent there instead.