The RSS Blog

Michael Heileman: It appears that RSS enclosures should not contain an FTP link.

http://techlifeblogged.blogspot.com/2005/08/question-about-rss-enclosures.html

Randy: According to the spec, url must be http, it cannot be ftp, it cannot be https, nor any other URI scheme. That doesn't prohibit podcatchers from accepting other URI schemes, but for interop, stick with http.