THE 3 KEY STAGES OF OUR EMAIL VERIFICATION PROCESS
We check the overall syntax of the email address to see if it is correct, e.g does it contain an @ sign or any invalid email address characters?
We then check the domain to see if it exists, and is it configured to accept email? then we’ll look at the mailbox, the part before the @ symbol.
Finally we check the mailbox, the part before the @ symbol, directly with the ISP, in this case Hotmail, to see if the mailbox exists or not.