Microsoft has publicly apologised for a three-day service outage on its Outlook.com and SkyDrive services.
In a service status update on its website, Microsoft said:
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"We want to apologise to our customers who were affected by the outage on Outlook.com... We have restored access to all accounts and have made changes so that the service will be more resilient in the future.
"We realise that we have a responsibility to the customers who use our services to communicate and share with the people they care most about, and we apologise for letting those customers down this week."
Microsoft blamed a "failure in the caching service that interfaces with devices using Exchange ActiveSync", which includes smartphones, and admitted that the downtime affected "sharing features of SkyDrive" as well as the Outlook servers.
Downtime was reported widely across Microsoft's userbase from 14 August to 17 August. Microsoft explained that some customers were affected for longer than others due to a build-up of backlogged Exchange ActiveSync requests that had bottlenecked in the system after the initial caching service failure.
The company said that, in future, it will increase network bandwidth in the affected part of a system should a similar problem occur, and will change error handling protocols for devices that use Exchange ActiveSync.
Microsoft is currently scouting out options for a new name for its SkyDrive service, after a legal settlement with satellite broadcaster BSkyB in which the company complained that the name of Microsoft's cloud platform was too similar to its own service.
BSKyB has granted Microsoft continued use of the name "SkyDrive" for "a reasonable period of time".
