I think that the author is a bit confused about email validation. When I was doing this, via email, if you wanted a certificate for sub.subdomain.example.com -

I think that the author is a bit confused about email validation. When I was doing this, via email, if you wanted a certificate for sub.subdomain.example.com - the list of email addresses were in order something like hostmaster@sub.subdomain.example.com and hostmaster@example.com - you clicked the radio option that best suited you and you were good to go. You don't need email addresses for every subdomain.