Syntax Check-Validates the address for syntax, whether it has all of the mandatory characters present (e.g. @) and any illegal characters present (i.e. ~). It will also check for multiple occurrences of required characters (i.e. @@). DNS/MX Record Check-Validates the domain name with DNS server to ensure that the email domain is a valid registered domain. Mail Server Check-Validates an email address (e.g. [email protected]) by mail server (e.g. mail.hotpop.com) to ensure that the mail server indeed has the email address. This method has very good performance. (Attention: a few mail servers don't support this method(e.g. yahoo))