Hi, my name is Arthur de Haan and I am responsible for Test and System Engineering in Windows Live. To kick things off, I’d like to give you a look behind the scenes at Hotmail, and tell you more about what it takes to build, deploy and run the Windows Live Hotmail service on such a massive global scale.
Hosting your mail and data (and our own data!) on our servers is a big responsibility and we take quality, performance, and reliability very seriously. We make significant investments in engineering and infrastructure to help keep Hotmail up and running 24 hours a day, day in and day out, year after year. You will rarely hear about these efforts – you will only read about them on the rare occasion that something goes wrong and our service has run into an issue,.
Link – http://windowsteamblog.com/blogs/windowslive/archive/2009/12/22/a-peek-behind-the-scenes-at-hotmail.aspx