A new service was added to the Windows Live Beta family today - Windows Live Custom Domains. The basic idea is that anyone with a domain can now point their MX record to the Live servers. What that means is that users can have Microsoft's servers hosting their own domain's email accounts for free. There's a restriction of 20 email accounts per domain, with each mailbox getting 250MB of space.
In addition, the same account functions as a Passport account, and can be used to sign in to MSN Messenger, MSN Spaces etc. I'm assuming users also get access to the spiffy, new AJAX-enabled Windows Live Mail Beta service as the webmail frontend for all their accounts, although that isn't explicitly mentioned anywhere on the site. The team that's working on this also has an official blog, just like all the other Live teams do.
View: Custom Domains Blog