code: public static void addEmailDataTransportListener (@Nonnull final IEmailDataTransportListener aEmailDataTransportListener)
    {
      ValueEnforcer.notNull (aEmailDataTransportListener, "EmailDataTransportListener");
      s_aRWLock.writeLocked ( () -> s_aEmailDataTransportListeners.add (aEmailDataTransportListener));
    }
docs: Add a new mail transport listener.
  
  @param aEmailDataTransportListener
  The new transport listener to add. May not be <code>null</code>.
  @since 1.1.0