I've had a Hotmail/MSN/Live.com email account for awhile now, and it's been relatively spam-free. Of course, that address is not published anywhere, and I hardly ever use it, so I would expect that to some degree. 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 I send myself an email from my live.com account, it arrives speedily, and my reply is delivered back to the live.com account almost instantly. But if I then write a new message to the live.com account, it never appears, even though it came from an address that I just emailed.
Thus, Microsoft is simply deleting legitimate emails. Why would I bother using such a service? It's like buying a car that will only start once in awhile, or a refrigerator that keeps the soda cold, but lets the milk go bad. It's useless.
I'm not alone here, either. This thread at MozillaZine goes back to 2006, and describes these exact problems in excruciating detail, among others. Ian Gregory has also been cataloguing this problem for a few years now.
The temerity of Microsoft to simply never deliver these emails is shocking to me, but taken in concert with my original point that Microsoft software forms the very core of the spam problem to begin with, and the only conclusion I can make is that they are waging a war -- not against spammers, but against email.
Perhaps they're going to unleash some hidden features in Exchange 2008 that will ensure that email sent from one Exchange server to another is always passed through (and always reaches hotmail.com, msn.com, and live.com addresses), leaving everybody else out in the cold -- a Frankenstein thought if there ever was one.
Their motive may be unclear, but their actions are transparent -- they are complicit in the generation and distribution of spam, and are summarily deleting emails addressed to their users under the guise of fighting spam.
Until they remedy this egregious activity, I've instructed my mailservers to discard any inbound email from hotmail.com, msn.com, or live.com.
In a few days, I probably won't be able to reply to them anyway.