I am fed up with people doing stupid things when checking email addresses on web forms. Apparently other people are too...
The main thing that really gets on my tits is this...
+ is an allowed character in an email address, for example:
firstname.lastname@example.org (is an email address)
email@example.com (is the same email address with a +randomthing tag which helps people filter their mail appropriately, and saves people creating different email aliases for things.)
Far too many web forms do utterly stupid "sanity" checks on the email addresses entered, and are just wrong.
Stop it you fucking morons, read the RFC. It is the RFC that tells us what makes an email address acceptable or not, not whatever magical idea just popped in to your head. They're called standards for a reason.