Redmine

Since all html tags are strips on html-only emails, they almost never work.
I would suggest using Loofah to convert html content to plain text.

Patch (works on my installation):

    if plain_text_part.nil?
      # no text/plain part found, assuming html-only email
      # use loofah to extract text
      @plain_text_body = Loofah::HTML::Document.parse(@email.body.to_s).to_text
    else