opennap is the old napster network, just the servers are run by different people rather than a company like napster - winmx started out as an opennap client before adding its own network
https://www.winmxworld.com/tutorials/opennap.htmlwith winmx any messages are sent to you directed at the IP Address and UDP port of the primary user you are currently connected through (addressed to your username so it knows who it's for), when you reconnect you reconnect through a different primary, so that old contact info for you (where to send the data) is now invalid - so you can't have a permanent entry in the host list
in theory if you ran winmx on primary yourself, and had a static IP Address then it would be possible for it to use permanent entries, however if it allowed that then it would just end up confusing people... as it is though it changes the ID on the end of the username anyway so even on primary you can't be added permanently (if it had the option to do so)