Sorry, there's no way to limit downloads to a single email address because a download doesn't involve an email address at all. A file is downloaded via a browser, not an email client.
We do limit the number of times a download link can be used so that a buyer who purchases for themselves cannot share that link with the public at large. If the download is for a PDF that we are stamping, the original buyer's email address will be stamped on the file, further discouraging them from sharing the file itself.