Huge. Here is some data from a PDC Hotmail presentation:

  • ~200 million active users
  • 3.3 billion inbound emails a day
    • 1.5 billion blocked at the router
    • 1.0 billion deleted as spam (never hits the user's mailbox)
    • 0.5 billion sent to the junk folder
  • Over 100 million messages sent a day
  • 80 - 100 milllion logins per day
  • 5000 peak logins per second

    But the most interesting part in this PPT is the new FrontEnd design. It is based on the Atlas framework. The client code (Javascript  - in the browser) is able to call into front-end components (written in C#). The requirements for the protocol are interesting: minimize the data on wire, purely asynchronous processing at the server side. All this combined with an OOP component framework.