Returning letters is sometimes necessary when you receive a letter that has been sent to the wrong address. For example, this can happen if a letter is addressed to the person who lived in the room before you and the sender does not know that they have moved out.
If you receive a letter like this, you should send it back to the sender. Returning letters is free to do. First, cross out the name and address on the front of the letter. You do not have to cross out the barcode at the bottom of the envelope. Next, write “retour afzender” (return to sender) on the front of the letter and post it. It is now the responsibility of the sender not to use your address anymore. For more info visit post.nl (only in Dutch).