 
   ## Provider options
 
-  - `:custom_vars` (v:)
-  - `:sending_options` (o:)
+  - `:custom_vars` (used to translate to `v:`, now `h:X-Mailgun-Variables`)
+  - `:sending_options` (`o:`)
   - `:template_name` (template)
   - `:recipient_vars` (recipient-variables)
-  - `:tags` (o:tag, added before `:sending_options`)
+  - `:tags` (`o:tag`, was added in before `:sending_options`)
 
   ## Custom headers
 

  defp prepare_html(body, %{html_body: nil}), do: body
  defp prepare_html(body, %{html_body: html_body}), do: Map.put(body, :html, html_body)

  defp prepare_template(body, %{provider_options: %{template_name: template_name}}), do: Map.put(body, "template", template_name)

  defp prepare_template(body, _), do: body



  defp encode_body(no_attachments), do: Plug.Conn.Query.encode(no_attachments)

  defp encode_variable(var) when is_map(var) or is_list(var),
    do: Swoosh.json_library().encode!(var)

  defp encode_variable(var), do: var
end
