However, some tests I ran over the weekend shed some light on some of the ways that Hotmail/MSN/Live.com handle spam: They apparently are simply deleting inbound email with no bounce messages, no flags, no notification — nothing.
I can replicate this at will. When I send an email from my mailserver (located on a commercial circuit) to my gmail.com account, live.com account, and other personal accounts, they all arrive — except to my live.com/Hotmail account. It simply never appears, and no bounce message is ever seen.
If Microsoft is really dropping legitimate emails without any notification to the sender or the receiver then, well, it is time to drop Microsoft mail services.