you'll need to tune the page's timeout if you try to parse the user's email address and attempt to resolve a webpage for the domain as some lookups can take a little while, also, a number of ISPs don't have domain names that map to the user's email domains, and some providers use a subdomain for email that has no website counterpart, and I doubt you want to parse MX records from DNS and read DNS records to find the domain A or CNAME records which may or may not tie to a website.
you are probably better setting a flag in your database for new registrants an that says it is unverified address and send the user an email with a link that they can click to verify their email address.