After a client send a "forward me a message" request to the server, it waits for the server to respond. This could be forever if the server is down.
The message format is clunky and not very sophisticated.
Binary data can not be transmitted. (This is probably a good thing.)
The "forward me a message" request does not need a receiver address. It is built into the request message. In fact, using the receiver address field, a client (message requester) can trick the server into sending someone else a message.