[DZittersteyn]

This is answering the question: "Does tihs email address exist?", which is nice, but usually not the question being asked. The more common question is "Is this the email address of the user", which can only be answered by a confirmation email.

You could use this method as a first-line validation though, to give the user some feedback (similar to not implementing the full RFC regex, but simply checking /.+@.+\..+/)