Microsoft just announced a new initiative that will include email 'caller-ID' type technology that will allow an email server to verify the sender prior to accepting the message. This has the potential to be huge in the fight agains spam and spoofed domains. Hopefully this gets done right (open standards are used) and is accepted across the industry. This is similar to the SPF technology I posted about earlier in the month.
Q&A: Microsoft's Anti-Spam Technology Roadmap