It's not a secret. Lots of times you would get an instant ban the moment you signup with a hotmail account, even with a fresh new IP which clearly does not have bad reputation or whatever. And interestingly enough, you merely get any problem at all with gmail accounts. The thing is, aren't hotmail the second largest free email service provider(with over 360 million users)? So why are tumblr so angry that they'd rather mistakenly ban real users instead of targeting more accurately to spammers? I really don't get this, but why?