Yahoo CEO Marissa Mayer wrote a blog on Tumblr saying how “very sorry” she was for the inconvenience and frustration the Yahoo outage caused to its users. She also explained the cause of the very long “scheduled maintenance.”

While Yahoo Customer Care had been very considerate on responding and updating the Yahoo users of the status of the outage through its Twitter account @YahooCare, the company chief still felt the need to apologize to their services’ users greatly affected by the outage. Mayer did a brave move to speak for her company and to admit the problem.

She began her post with: “This has been a very frustrating week for our users and we are very sorry.” She also admitted: “We really let you down this week.”

Mayer explained that the outage began December 9 at 10:27 p.m PT when the engineering team reported that one of the servers went down due to hardware issues. The initial problem affected one percent of the users. They immediately worked on resolving the problem and thought that they can have it up again by the following day. However, that wasn’t the case.

Several users had different issues and they had to resolve each. Users had reported to Yahoo Care that they were unable to login, some were seeing scheduled maintenance page, and some were able to login but their messages won’t send to the recipients.

Yahoo had finally found a fix. CEO Mayer wrote: “We worked around the clock to restore 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.”

Mayer confirmed that almost 99.9 percent of the affected users had their services restored and backlog messages were being sent to the recipients. They are still working on the full restoration of the inbox service.