def send_update(event, client)
      begin
        EventMailer.appointment_update(event, client).deliver_later(queue: "low")
      rescue Net::SMTPAuthenticationError, Net::SMTPServerBusy, Net::SMTPSyntaxError, Net::SMTPFatalError, Net::SMTPUnknownError, Net::OpenTimeout
        flash[:success] ="There was an error with the email server. No email was sent to #{client.name}."