Apache and other open source groups are concerned over patents filed by Microsoft concerning Sender ID, which is intended to be a way to positively identify the senders of email.

Many of the license provisions worry open-source developers. According to an analysis done by Larry Rosen, general counsel of the Open Source Initiative, Microsoft’s License would require mail-service providers incorporating Sender ID into their products to tell Microsoft about customers using it. The software giant also has not informed the IETF of potential patents pending on the technologies, and the license is not compatible with open-source development groups and requires users to be subject to U.S. export control laws, the analysis stated

Unless there is some change in the licensing structure, this move clearly puts a kink in the armor of Bill Gates plan to rid the web of spam within two years. Apache is used by a significant number of servers all over the world, so gaining the open source and Apache support for the Sender IP is important.