Hotmail - the Genesis planet for spammers...
"Microsoft appears to be the only big player that has really been serious about fighting the spammers."
Are you KIDDING me? FIGHTING the spammers??? Hotmail FEEDS the spammers! Try this simple experiment:
(a) Set up a Hotmail account such as firstname.lastname@example.org using a browser on an (uncompromised!) PC;
(b) Don't actually use the account or even give the address to anyone;
(c) See how long it takes for spam e-mail to start to fill it up;
(d) errmmm... that's it.
My guess is either that Microsoft's systems are even more broken than Windows itself, or that selling lists of customers' e-mail addresses provides a useful end-of-month bonus for lowly underpaid MS IT staffers.
The ONLY step that I've known Hotmail to take in order (allegedly) to address spam was when they suddenly decided unilaterally to reduce MAX_RCPT on their SMTP mail servers to 10 from 100 without telling anyone (or even admitting it), despite 100 being the minimum according to IETF standards... see here:
Oh, and if you access that link, note that Hotmail admitted that 90% of their inbound mail was spam... 4.5 billion messages out of 5 billion! No wonder, if some insider is flogging off address lists...
* This doesn't actually affect us, as we run our own mail servers and block** all e-mail from the Hotmail and Live domains.
** In this part of the known Universe, senders using such accounts should of course get the polite "550 rejected" message from us explaining why. But as Microsoft ignores all open standards in favour of their own home-brew versions, it looks as though MS doesn't bother delivering these... :(