You say you need to validate an e-mail address, to what contex do you wish to validate?
The obvious and simplest validation is the format.
Analyse the string that is the e-mail address, for correct format.
Does it follow the format of <username> @ <domain>, that is fairly simple to do.
The hardest part is to actually check the string given, once satisfied that the string given is an address in the correct format, start a different process / procedure to PING the address string given. If returned error then obviousley NOT a valid email.