I acquired an existing small website not too long ago. When I went to register the domain on google apps, it turned out the domain was already registered and I would need to contact whoever had previously set it up. Which turned out not to be the folks I acquired it from, but instead the original owner who had transferred the site to them.
He told me when he originally sold the site, he retained the rights to the MX records. Why would anybody want to do this? He hasn't been associated with the site in years. Is this a common practice?