News.com: End of the road for SMTP?:

“Some of those tackling the problem are looking at amending protocols other than SMTP. Microsoft, for example, advocates a change to the domain name system (DNS) that would make it harder for spammers to disguise their identity.

The DNS is a distributed database, maintained by a number of different companies that provide domain names for Web site and e-mail addresses. The problem with the system, spam-fighters say, is that like SMTP, it provides no system for authentication.

‘One of the things we want to do is attack this issue of spoofing,’ said Harry Katz, program manager of Microsoft’s Exchange server group. ‘That’s job one, in terms of putting a curb on spam, and we think we can do that (by) making a minor enhancement to the DNS.’

The ‘minor enhancement’ Microsoft is preparing to release would let individuals, companies and other organizations publish the identification numbers of their mail servers in the DNS database.”