In src/mud-telnet.c:671, the function mud_telnet_send_sub_req (and subsequent function mud_telnet_send_raw) sends data one byte at a time. Everywhere it's used, it's got a fixed size sequence to send, so it would be relatively trivial to fix this.

That's one byte per packet. That's a 4000% overhead. (Granted, these things aren't sent very often...)

Furthermore, it's much more convenient on the server side if short options are sent in a single packet. Multiple packets means multiple calls to receive(), forcing another layer of buffering or more complex buffering, etc.