Probably a very oceanic answer you are expecting. Verification of email happens at client side to check whether the email has been given correct or not (checking the validity of @ and . dot).
But to my knowledge, whether the given email is existing or not can only be known after your message hits the destination domain. When the server doesn't find the domain name to which you have sent the email the same will be bounced back (mailer-daemon). It MAY NOT be possible to verify, infact identify may be correct term, whether the email you have given is a valid existing email or not.
Rk