When setting up a new account, updating your email address, or inviting an applicant, our system checks the email address to make sure it exists. If the email host for the provided address says the email does not exist, then that means an email can not be delivered to the address provided.
This is a simple way to help prevent mistyping email addresses in the system. You'll need to make sure the email address is active and exists. If the email address was created within the past 24 hours, the mail server may not have access to tell us it exists yet.