http://www.itu.int/osg/spu/spam/chairman-report.pdf
18. Identification standards are being developed by a number
of industry and standards groups, such as IETF through
its MARID group, as well as by Internet Service
Providers, which are trying to collaborate to limit the
spread of spam. Although authentication systems are
deemed to be a critical part of the solution, their
implementation remains problematic, and the wide
adoption of a standard authentication method seems far
away. Furthermore, the cost of technical solutions, the
level of technical support necessary and the need for
continual updating, present cost issues for developing
countries, their ISPs and their users.