电子邮件验证PHP

I have the following code which (I think) will only verify the domain of the email address.

$EmailAddress = "user@domain.com";

list($User, $Domain) = explode("@", $EmailAddress);
$DomainExists = checkdnsrr($Domain, 'MX');
if($DomainExists==true){
    // Email domain exists
}
else{
    // Email domain does not exist
}

If I can, how do I verify the $User part?

The only guaranteed way to make sure user@example.com exists is sending them an e-mail with a verification link.

Here's another post on how to do that: Easiest way for PHP email verification link

The only way you can tell if an email address exists is to send email to it with a task for the user to perform (usually clicking on a link), for the email not to be caught in spam filters, and for the recipient to perform the task.