This works for walled gardens like Reddit, HN or Facebook. If the content is really distributed (think for example SMTP or NNTP) there's no way to reliably reca

This works for walled gardens like Reddit, HN or Facebook. If the content is really distributed (think for example SMTP or NNTP) there's no way to reliably recall something that has been posted. In this case it is up to each node to make the decisions what content they keep and what remove (and who they give the authority to make these decisions).