eWeek reports that MARID dumped Microsoft, and has instead opted for a hybrid solution for sender-authentication using SPF with modifications for checking other header fields (a variation of United SPF). The Microsoft extensions were patent encumbered and although a royalty-free license was available, obtaining the MS license agreement was a concern for the open source community. The Apache Software Foundation published an open letter a couple of weeks ago stating they would not be implementing Sender ID in their products under the MS license agreement.