Following up ECM theme: Mystic "RedirectUrlPage.aspx" is added to links when "href" property starts from url not equal to BaseUrl. RedirectUrlPage does nothing but returns 302 redirect code and adds "Location" header with value that is taken from real url. I've also found out how really ECM works when sends messages - it creates a link to download (see previous post), then this link is just processed as each standard request to Sitecore, with all pipelines, and returned output is being processed by several methods like replacing tokens and link modifications. Then output is being sent to subscribers.