Possible Duplicate:
PHP email validation function
How to check whether a email is valid or not in PHP?
Possible Duplicate:
PHP email validation function
How to check whether a email is valid or not in PHP?
You can only really check if an email address is valid by actually sending an email to it and checking for the return code from the SMTP server.
GO to http://en.wikipedia.org/wiki/Email_address#Syntax
I use a PHP function on my site that checks for all those parameters.