An update on my Hotmail problem. About 36 hours after fighting my way through their torturous help system in order to send an email asking for aid, I got a reply from an actual human.
She was profusively nice. Almost too touchy feel-y, with constant talk about my "frustration" and "feelings". Anyway, here's her explanation of when they request validation:
Now, I'd like to let you know when you will be requested to validate your usage of your Hotmail account, they are:
1. When you access your account or send a message through the web interface
2. When you access your account through your e-mail client
3. When you lose the ability to display your messages in your e-mail client
Is it just me or does this translate into being constantly asked for validation at every turn, i.e. 50 times a day, as was my problem? She goes on to say that this policy is part of a process aimed at creating a "really Spam-free Hotmail" and that "after a certain period, this challenge will diminish significantly and will only happen periodically because the system will recognize you as a legitimate customer."
I don't know about the ethics (or effectiveness as a business practice) of forcing your users to prove that they are "legitimate customers" rather than simply treating them that way in the first place, but there has been one upshot. Even though she didn't say anything about it in the email, the spam from them has mysteriously stopped. I guess begging to be left alone was a human enough trait it proved to them definitively that I'm not a spam bot. At least for now.