Yes, you can write “return to sender” on the package and place it back into your mailbox. However, this is typically not the preferred method. If the addressee does not live at your address, then you should write "not at this address" on the package. If the package is addressed to you but you simply do not want it, then you should write "refused" on it. Following these rules makes it more clear why the package is being returned, and it can help avoid improper deliveries in the future.