code: public static void addConnectionListener (@Nonnull final ConnectionListener aConnectionListener)
    {
      ValueEnforcer.notNull (aConnectionListener, "ConnectionListener");
      s_aRWLock.writeLocked ( () -> s_aConnectionListeners.add (aConnectionListener));
    }
docs: Add a new mail connection listener.
  
  @param aConnectionListener
  The new connection listener to add. May not be <code>null</code>.
  @since 1.1.0