What has 1.3 billion inboxes, 155 petabytes of storage and 350 million monthly users?

Microsoft currently hosts around 1.3 billion Hotmail inboxes, according to statistics just released from the software giant, that make fascinating reading for anyone interested in an at-a-glance look at the once-seminal webmail service.

In a blog post, Microsoft says it's offering a "look behind the scenes at Hotmail" telling consumers about "about what it takes to build, deploy and run the Windows Live Hotmail service on such a massive global scale".

"You will rarely hear about these efforts", pouts Microsoft.  "You will only read about them on the rare occasion that something goes wrong and our service has run into an issue".

Describing the service as "gigantic in all dimensions", Microsoft says Hotmail is available in 59 regional markets, and in 36 languages with over 350 million people actively using Hotmail on a monthly basis.

Hotmail sees over 3 billion messages sent a day with 1 million filtered out as spam, with those 1.3 billion inboxes requiring storage of over 155 petabytes, a figure that grows by more than 2 petabytes a month (to put this in context, a petabyte is 1 million gigabytes)

These highlights are followed by information on Hotmail's architecture, engineering, testing and deployment, all of which can be found on the Microsoft blog post.