NSC does not permit web based email addresses to be used for new registrants. We do this as users often seeking to be malicious and/or abusive often try to hide behind the anonymity that a web based email address provides.
So, if you try to register using one of the common web based email providers such as Hotmail or Yahoo, the board will tell you your email address is banned. Don't take it personally - you could be Bobby.Zamora@hotmail.com, or Dick.Knight@Yahoo.co.uk - it makes no difference - you're not getting in unless you use a 'real' email address.
Of course, there are many hundreds of web based email providers out there and it would be difficult/impossible to block them all. However, we regularly review our 'banned' list and adjust as required.
Whether you use an ISP assigned email address, or one you have via your place of work you can rest assured that all email addresses in NSC are held securely, not disclosed/passed on or sold to any other organization and you will not receive spam as a result of registering with NSC.