Email addresses are publicly viewable on the NNQL webpages - spam harvesters can pick these up. There are a number of different methods that you can use to hide the address from bots.
I have been thinking about that for a long while. While i don't got access to the NNQL site, i removed the email addresses from the EQL site at least. I think the IRC channels are enough to organize games anyway.
Show them only if the user is logged in.