.banQ: mode # +b ~q: $+ $address($1, [color:blue]2)[/color]

2 is the mask type (in this case, *!*@host). See /help $mask for a complete list.

Note that $address() is IAL-dependant (/help IAL), which means it will fail if mIRC doesn't already know the full address of $1.

You can use Iori's code to update the IAL as soon as you join a channel.