@nixCraft Everytime someone uses a regex to validate an email, god kills truckloads of kittens
Split on last @ ensuring the previous character is not itself an @
Check if the domain part resolves, make sure you allow for international domain names.
You can check if the localpart is well formed. IIRC this is not possible with regexes. You need a parser.
With a valid domain, sending an email is the only real way to verify if the address is actually valid. Well formed doesn't mean accepted.