Transform email content by applying an XSL transform to it. It should be noted that since e-mail content may
actually be a collection of XHTML fragments instead of well formed XHTML this MailContentProcessor will
temporarily wrap the content in a root element called "temporaryFragmentRootElement" which is automatically removed
after processing. You need to be aware of this element to ensure the XSL template configured for this
processor handles (and ignores or passes unchanged) this temporary element.