Any system that includes an SMTP server supporting mail relaying or delivery MUST support the reserved mailbox "postmaster" as a case- insensitive local name. [...] The requirement to accept mail for postmaster implies that RCPT commands which specify a mailbox for postmaster at any of the domains for which the SMTP server provides mail service, as well as the special case of "RCPT TO:" (with no domain specification), MUST be supported.
SMTP systems are expected to make every reasonable effort to accept mail directed to Postmaster from any other system on the Internet.
Microsoft appears to have stolen most of the product of a somewhat small microblogging or "micromessaging" startup called Plurk. I use Plurk: it's in a little widget in the sidebar. I also have it gated to Twitter. It's free. Microsoft wanted to start a competing service in China called "Juku," so they helped themselves to most of Plurk's work. Maybe that's how they think open source is supposed to work. :(
On the one hand, I guess M$ could solve all this by exercising more capitalism and buying up Plurk with their scads of cash. On the other hand, I don't know if I'd want that to happen. Plurk, for their part, does have their ownthoughts on the matter. But I bet this whole thing disappears pretty quickly, one way or the other. For Plurk, I hope that disappearance goes as well as it can for them.