Microsoft's (NASDAQ:MSFT) efforts to win support for its updated cloud-based email system, Outlook.com, hit a snag earlier today. An unexpected flaw led some servers to overheat, cutting service to an indeterminate, but substantial enough group of customers, that Mr. Softy saw fit to disclose the problem in a blog post.

According to Microsoft vice president Arthur de Haan, the company pushed new firmware -- i.e., code designed to update the underlying chips and hardware -- to several of its servers in a key datacenter. That's when the trouble started.

"This failure resulted in a rapid and substantial temperature spike in the datacenter. This spike was significant enough before it was mitigated that it caused our safeguards to come into place for a large number of servers in this part of the datacenter," de Haan wrote.

As a result, the system denied access to a number of mailboxes hosted on those servers. Microsoft's cloud hosting service, SkyDrive, was also affected for a time. The outage lasted 16 hours in all.

Previously known as Hotmail, Outlook.com had as many as 360 million users last year, making it the world's second-largest online email system. Google ranked first with more than 425 million Gmail users worldwide, according to the latest figures available.

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