email address validation should not be motivated by what is valid address by some RFC, but what you feel confortable passing to your MTA, because you have exact

email address validation should not be motivated by what is valid address by some RFC, but what you feel confortable passing to your MTA, because you have exact understanding of what will happen. On the application side you probably don't want to store adresses with comment and real name fields and other such only human readble data. My rules are: contains exactly one @, contains zero or more +, does not contain any other characters that are special cased by this (notably ',', ';' and '!').