As a side note (and to add a small bit of extra info), this is available in the help file:
"With the Normal method, mIRC relies on your winsock to reply with the correct information.
With the Server method, mIRC looks up your local host through the IRC Server, and then performs a /dns on it to resolve it to an IP address.
The Server method will most likely be slower, you can tell when it has been completed when you see your local host name and IP address displayed in the status window."
See /help local info.