Out of interest, why would you need such a stringent e-mail address check? Assuming that you want it to be a correct e-mail address so that you can e-mail your users, it might be worth implementing an e-mail confirmation system where you e-mail your new registrations and they then click the link to confirm their e-mail. This would catch the people who just enter junk but regex valid email addresses (ie, bill@microsoft.com) when registering.

Unfortunately, a problem I ran across recently was users using sites like MintEmail - Disposable/Temporary Email Address (temporary 4hour throwaway e-mail addresses) when registering - short of banning all these domains I have yet to find a solution to this.

Alan