Deutsche Post has announced that keys that have been thrown in unpackaged will no longer be delivered in the future. In the price list states that the product “KEYS DELIVERED UNPACKAGED will be discontinued on 12/31/2024”.
So far, it has been possible to simply throw found keys that have a tag with an address that can be delivered to a mailbox. The recipient has to pay a fee of 8.50 euros for the delivery. This is usually much cheaper than duplicating a key or even replacing the lock.