Marissa Mayer issued an apology on Friday after a hardware outage prevented some of its users from accessing Yahoo Mail for almost a week. On Monday, December 9th at 10:27 p.m. PT, Yahoo's network operating center alerted the Mail engineering team to a specific hardware outage in one of our storage systems serving 1% of Yahoo's users. Yahoo's engineers initially estimated that full recovery would be complete by 1:30 p.m. PT on Tuesday. But according to Mayer, the problem "was a particularly rare one, and the resolution for the affected accounts was nuanced since different users were impacted in different ways."

Some of the affected users were unable to access their accounts, instead seeing an outdated "scheduled maintenance" page which was a confusing and incorrect message. Further, messages sent to those accounts during this time were not delivered, but held in a queue.

Yahoo eventually restored access and all messages to inboxes. This has included restoring IMAP access for people using other email programs like Outlook or Apple Mail to access their Yahoo Mail. As of Friday afternoon, Yahoo had restored access to almost everyone and delivered the backlog of messages. The company will continue to work on rolling out IMAP access and to fully restore inbox state (for example, which folders messages were placed in, which messages were starred, etc). Mayer says this process differs for each user and as restoration continues, proomising to communicating directly with users on progress on an individual basis.

"This has been a very frustrating week for our users and we are very sorry," Mayer said. "We're going to be working hard on improvements to prevent issues like this in the future."