Sender ID is an anti-spam proposal from the MARID IETF working group, joining Sender Policy Framework and Caller ID.
The Sender ID proposal is currently the subject of controversy regarding intellectual property and licensing issues: Microsoft holds patents on key parts of Sender ID and licenses those patents under terms that are not compatible with the GNU General Public License and which are considered problematic for free software implementations in general by free software groups like the Apache Software Foundation and the Debian project .
The MARID IETF working group has stopped their work on the new standard because of major differences between the members of the group on 2004-09-23.