Gary Numan wrote:What is an 'open letter', as opposed to, say, an editorial, article, blog post, etc.?
An open letter may be issued as an editorial, an article, a blog post etc. It may be published in any public network and social network media or in newspapers.
English edition of Sepp Holzer's open letter was published in Space of Love magazine, issue #2, in January 2009: https://ecominded.net/sol-magazine