A new beta service has popped up at Microsoft's Live.com today. It's called Windows Live Custom Domains and it enables you to have your domains hosted for e-mail and IM by pointing your MX DNS records to Microsoft's servers.
Create up to 20 e-mail accounts within your domain
Get up to 250 MB inbox for each account
Check your e-mail from any Web-enabled PC
Junk e-mail filter protection using Microsoft SmartScreen technology
Virus scanning and cleaning of e-mail
Seamless access with MSN Messenger, MSN Spaces, etc.