The easiest and most robust way to deal with email is to have 2 fields. string email, bool isValidated. (And you'll need some additional way to handle a time based validation code). Accept the user's string, fire off an email to it and require them to click a validation link or enter a code somewhere.
Email is weird and ultimately the only decider of a valid email is "can I send email to this address and get confirmation of receipt".
If it's a consumer website you can so some clientside validation of ".@.\\..*" to catch easy typos. That will end up rejecting a super small amount of users but they can usually deal with it. Validating against known good email domains and whatnot will just create a mess.
Email is weird and ultimately the only decider of a valid email is "can I send email to this address and get confirmation of receipt".
If it's a consumer website you can so some clientside validation of ".@.\\..*" to catch easy typos. That will end up rejecting a super small amount of users but they can usually deal with it. Validating against known good email domains and whatnot will just create a mess.