problem whit emails and dnslookup

[hacedordeestrellas]

hi guys, i have a problem. i have a service who allow to the admin send emails to them users. But whit the time a lot of people changes emails, or when are registering gives a invalid email adress. so, i want to can validate the email in the registration but IF THE EMAIL EXIST. can anyone help me please?. (e-mail address removed)

PD: excuse my english =).-

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