Yahoo CEO Marissa Mayer says she was "very sorry" for last week's Yahoo Mail outage, which she implied has affected roughly one million users.
"This has been a very frustrating ... for our users and we are very sorry," she said in a post on Tumblr, adding that, "we really let you down this week."
Reports surfaced late last Monday that Yahoo was having some major issues with Yahoo Mail, one of the company's most important services with about 100 million daily users.
Yahoo confirmed the outage at the time but details were sketchy about what caused it or how many people were affected. Mayer's post Friday sheds a little bit more light on the fiasco.
"Unfortunately, the outage was much more complex than it seemed at first, which is why its taking us several days to resolve the compounding issues," she wrote.
Yahoo's Mail engineering team was alerted Monday night to a hardware outage in one of the company's storage systems serving 1 percent of Yahoo's users, she said. With around 100 million daily users, that implies about a million users may have been affected at the start of the week.
The Mail team immediately started working with storage engineers to restore access and move to back-up systems, expecting a full recovery by Tuesday afternoon, Mayer wrote Friday.
"However, the problem was a particularly rare one, and the resolution for the affected accounts was nuanced since different users were impacted in different ways," she wrote.
For instance, some people saw an outdated "scheduled maintenance" page while trying to log in to their accounts, which was an incorrect message.
As of the post Friday afternoon, Mail had been restored to almost everyone, Mayer said, and the backlog of messages had been delivered. The company will continue to roll out IMAP access and restore people's inboxes, including returning messages in folders and starring messages, she said.
"We're going to be working hard on improvements to prevent issues like this in the future," she said.
The problems are unfortunate, given how important Mail is to Yahoo. As one of its most prominent products, improving the service has been a focus to attract new users to the company.
But a good number of users were upset even before this week's problems. Yahoo Mail was given a redesign in October that provided it with a more Gmail-like interface. But it was poorly received by many, for both the design and for functions that were removed.