Microsoft's outlook.com webmail service suffered 16-hour long issues yesterday after a firmware upgrade at the company's datacenter went wrong. In a blog post detailing the outage, Microsoft reveals some customers couldn't access parts of SkyDrive, Hotmail, and Outlook. Although Microsoft has updated its datacenter firmware successfully previously, the regular process "resulted in a rapid and substantial temperature spike in the datacenter" due to an unspecified reason. The overheating was significant enough to activate Microsoft's safeguard process for a number of servers in the datacenter, preventing access to certain mailboxes.

A 16-hour outage is unusual for such a high scale web service, and Microsoft admits it required some human intervention to bring the services back online, thus delaying the restoration attempt. "Requiring this kind of human intervention is not the norm for our services and added significant time to the restoration," says Microsoft's Arthur de Haan. The company doesn't provide numbers for the amount of users affected, but during the outage period we found that the majority of our own mailboxes were unaffected.

Microsoft is in the middle of transitioning its Hotmail user base over to its new Outlook service. The company has suffered a number of outages since the start of the year, also impacting its Office 365 business service. With three significant outages over the course of 2013, Microsoft promises that it's "hard at work on ensuring this doesn't happen again." At a time when it's investing millions of dollars to market Outlook.com, the company can ill afford to suffer long periods of outages, especially when it's on the attack.