When looking at a domain name as part of an email address or URL, you simply do not get enough information from it. You can even go so far as visiting that URL and you still will not have enough information about the ownership of that particular domain. Most of the kind of information that you would want will be located in a WHOIS database. These databases are maintained by registrars and can provide information about the owners of a particular domain. To get the information from these databases, you need to run a whois query from a client application. PHP provides this kind of client application through the PEAR package.
PEAR has a class called Net_Whois that enables you to query a whois database. You use it like so: