It may have taken three days, but Microsoft has officially resolved its Outlook.com outage -- and it has both explanations and long-term solutions for affected email users. Trouble began with the failure of a caching service for Exchange ActiveSync. The resulting deluge of reconnection attempts promptly overwhelmed company servers; a slow recovery was necessary to avoid another meltdown, Microsoft says. To prevent repeat incidents, the tech giant is both upgrading its network capacity and implementing a more elegant error handling system. While the fixes likely come too late for some users, they suggest that Microsoft has learned a hard lesson about the fragility of online services.