The crappy regex solution is much faster than what you suggest, and will work 99.9% of the time. The time you spend doing it the right way will reduce your conversion rate because people will view your site as slow. In this case worse is better.
No, it's not. Every time you exclude a valid e-mail address, you lose or annoy a customer for no reason other than your own lack of understanding of the RFCs.
There are a number of steps that can be taken that don't involve broken regexps that filter out valid addresses. Please stop trying to justify doing it completely incorrectly.
