Microsoft has said that the 14-hour Outlook.com and Hotmail outage was the result of overheating at one of the company's datacenters. The heat apparently resulted during a regular firmware update that ended up functioning in an "unexpected way." The outage was limited to just Hotmail and Outlook.com thanks to Microsoft's automatic safeguards that kicked in.
The outage started at 3:35p.m. PDT on March 12 and lasted until 5:43a.m. PDT on March 13. The outage was unusually long because the fix required both software updates and "human intervention." Microsoft says that the latter requirement made the outage last longer than usual.
Microsoft issued an apology for the extended outage and added that they take outages "very seriously." After all, outages are the last thing Microsoft needs as people continue to flock to competing services like Gmail.