I have posted about this numerous times. If you browse the Hotmail forums, they were ablaze with people rightfully upset that Microsoft intentionally abandoned all third party clients (and even Outlook Express and Entourage!) by disabling Webdav that works perfectly well for 98% of the population. Their "replacement" is such a poorly implemented POP3 implementation that clients cannot easily support "leave on server" mode due to the lack of UIDL support, even though internally every message has a unique identifier.
I personally have been a Hotmail user for 15 or so years so this affects me as much as anyone. As everyone in the Hotmail forums has suggested, if you want a mail server that supports open standards and seems care about customer feedback, move to GMail.
We are going to retest with Hotmail in one of the next Beta 2.0 releases, but 1.0 will defiitely never have support