This has nothing to do with mIRC's settings
The problem is that the server you're connecting to is not able to reverse dns your hostname from your connecting IP
This either means there's a problem with your ISP's dns servers, or there is a routing problem between the IRC server and the dns servers themselves. Both of these issues are usually temporary.
type /dns 90.211.193.158, if that works, then it's the IRC server's fault. It should clear up eventually.
No mIRC setting can change what the IRC server decides to show for your hostname, it's completely up to the server. The lookup method will not affect this.
