HTTP status code when sending email failed

Note: I have read this but I still don't know how to go about building the sending email function correctly, so I ask this question. I need to know the HTTP status code to use when email sending succeed/failed, or if that's not the right thing to do, the right thing to do.

A POST request to my rails app will send an email.

If the email sending failed, what HTTP status code should I return to the person who send the POST request in my JSON response?

  def inform
    delivered = true
    begin
      UserMailer.new_comment(current_user, other_user, @note).deliver_now
    rescue Net::SMTPAuthenticationError, Net::SMTPServerBusy, Net::SMTPSyntaxError, Net::SMTPFatalError, Net::SMTPUnknownError
      delivered = false
    end

    if delivered
      # I use :created here because email is created
      render json: { delivered: true }.to_json, status: :created
    else
      # I use :service_unavailable here because email sending failed
      render json: { delivered: false }.to_json, status: :service_unavailable
    end
  end