Although Microsoft staunchly denies it, the rather reasonable and impossible-to-kill rumor is that they tried - and failed miserably - to convert the Hotmail webservers to Windows NT / IIS / Exchange in early 1998, soon after having acquired it. Anybody who's had any experience with internet services like Exchange or IIS under NT 4 is probably grinning like a villain right now at the very thought of trying to run a farm of several THOUSAND of them - it brings to mind the infamous Ellen Feiss "switched" ads for Apple; one imagines a glassy-eyed, tousled Hotmail admin looking earnestly into the camera, and gesticulating bewilderedly while saying "NT ate our server farm. All of a sudden everything turned blue and it went bip-bip-bip-bip-BEEEEEEP! And it was good server farm, too..."

All we know for sure is that, despite the constant barrage of articles in the IT press and even a few in the mainstream press, for three solid years, their gigantic premium email service continued running on Solaris and FreeBSD. But then in 2000, Microsoft began publishing whitepapers on "the conversion of Hotmail from FreeBSD to Windows 2000", supposedly as a great model for potential customers to follow in "ridding themselves" of open source products.

The whitepaper had possibly even more than the usual amount of FUD (Fear, Uncertainty, and Doubt) marketing tactics and outright lies; among the key motivations it lists for the positive benefits of migrating Hotmail's webservers from FreeBSD to Windows 2000 was language portability issues. Probably the best summation of how intrinsically ridiculous this was got summed up in a comment at Daemon News:

China and Japan are two important growing markets for MSN, so multibyte character sets had to be supported. FreeBSD lacked the necessary Unicode support. Yup, they got us there. I guess [typing] cd /usr/ports/devel/libunicode && make install [at a command prompt] is beyond the capabilities of Microsoft engineers.

Beyond the ridiculous elements of the "urgent reasons" present to convert to Windows 2000, pundits also noted very quickly that in spite of these published "migration" descriptions, FreeBSD was still running the majority of the serverfarm. Even the most impartial observer would have no choice but to conclude that either the "pressing need" to migrate was a fallacy, Windows was simply not capable of efficiently operating the server farm to specification, or both... and considering that the company that develops Windows was apparently unable to make it work well enough to justify migration, the validity of their whitepaper as a model for customers became pretty clearly even more suspect.

A year later, in early June of 2001, Microsoft specifically and categorically informed the Wall Street Journal that there were no more FreeBSD servers at Hotmail - only to get slapped in the face less than a week later when a suspicious FreeBSD developer investigated and proved otherwise. In 2002, the amusement continued when a network security outfit discovered an internal document server wide open to the public internet in Microsoft's supposedly "private" network, and found, among other things, a whitepaper written by the hotmail migration team explaining why unix is superior to windows.

But of course all this is history. It's 2003 now, and of course Hotmail is finally an entirely Windows 2000 shop - well, at least on the front end; nobody really knows about the database servers, and since they're a lot harder to fingerprint from the public internet, nobody seems to be all that concerned about covering it up either. But yeah, obviously after all of that, Microsoft has finally at least gotten rid of the open source stuff out at the front of the farm where any Joe with a web browser can check it out. ::coughs::