nospamproxy.de [1,2] has some good articles on anti-spam technologies and points out, that CallerID works in a very similar way to SPF, RMX and other protocols to verify the sending host. Microsoft introduced its CallerID at hotmail.com as you can test yourself:
# host -t txt _ep.hotmail.com
So from the technical side it seems that the CallerID(ea) is probably even behind what SPF is capabale of [3,4,5]. On the other hand, some argue, that Microsoft might to \”acknowledge Open Source without accepting some of the risks of being truly Open Source might bring\”:
This product may incorporate intellectual property owned by Microsoft Corporation. If you would like a license from Microsoft, you need to contact Microsoft directly .
From that perspective, the patent claims by Microsoft might be only defensive . Some searching for latest patents by Microsoft (Title or Abstract: spam, Applicant: Microsoft) only reveals four related patents, one of them published in January 2004 .
If – on a legislatory level – Microsoft intends to push its technology, one should point out to the governmental experts and commissions that there are already technical alternatives that should be taken in account as well.