First step performs “syntax” checks and ensure that each email address conforms to internationally set email standards (RFC). This also checks for correct formatting and for presence of any invalid characters are not present in the email addresses.
Second step checks for the domain name (the part after @)existence.
Next step checks that the domain has been configured to accept emails (MX record lookup).
The Last step is to check if the user(the part before @) exists. We initiate a connection to the mail server, retrieve the response and abort the process before an email is sent. Morphy Email Verifier cannot verify yahoo , hotmail and aol mailboxes since these ESPs has blocked the verification requests from all third party verifier softwares. It can verify all other mailboxes including gmail.