code: @Nonnull
    public static EChange removeEmailDataTransportListener (@Nullable final IEmailDataTransportListener aEmailDataTransportListener)
    {
      if (aEmailDataTransportListener == null)
        return EChange.UNCHANGED;
  
      return s_aRWLock.writeLocked ( () -> s_aEmailDataTransportListeners.removeObject (aEmailDataTransportListener));
    }
docs: Remove an existing mail transport listener.
  
  @param aEmailDataTransportListener
  The new transport listener to set. May not be <code>null</code>.
  @return {@link EChange}
  @since 1.1.0