what about this scenario: each client app has 20 public relay URLs and their md5 checksum, when the owner of new relay wants to add his/her relay to the relay list he/she should send a request to public relay owners, the public relay owners add this new relay URL and relay URL md5 checksum to a table on the relay servers . when a user adds a new relay URL, the client app searches relay URL and its md5 checksum in public relays table and if it was matched the client app adds the relay URL.