Integrate the freeware SpamAssassin spam-filtering software with Lotus Notes / Domino
When you receive an iCal invitation an error like this will be reported in the Notes Log. 08/01/2006 07:41:07 AM Router: Agent printing: SpamAssassin (mail\nradov.nsf): Message-ID has been converted to Rich Text and can't be checked for spam. You must change the format preference for incoming mail on the mail recipient's Person document to enable spam checking.