Dear E-Commerce Web Sites,
Before you get overzealous when validating email addresses, please do a bit of research. Wikipedia is a good place for general background (it’s also the first hit you get when you Google email address specification). For more in depth reading, one would obviously look at the IETF RFC 2822.
Notably, a plus sign (+) is valid in the local part.
And yes… it should be noted that the company I’m going to work for is guilty of this overzealous validation.