"This has been a very frustrating week for our users and we are very sorry," wrote Yahoo chief executive Marissa Mayer in a Tumblr post on Friday night. She was talking about the days-long outage that she said  left 1 percent of all Yahoo Mail users without access to their e-mail. While 1 percent might sound like a small group, given the 100 million monthly active users the service boasts, that means around 1 million people were left without access to their e-mail.

The outage was caused by a hardware issue in the storage system that serves Yahoo Mail, the company said. It blocked some users from being able to log into their account, and "messages sent to those accounts during this time were not delivered, but held in a queue." The issue started affecting users last Monday, Dec. 9, and the company initially estimated that they would have a "full recovery" complete by 1:30 p.m. PT the next day.

But the problem turned out to be much more complex than Yahoo initially thought,Mayer said in her post, and work to repair it continued through the weekend. In updates over the weekend, Yahoo said that "99.9% of affected users" regained access to their accounts and that it was "making steady progress on restoring access to messages." However, the company also said that incorrect time stamps on some messages may persist for some users.

And those users are not not happy. On The Switch's coverage of this story on Friday, many commenters threatened to leave the service over the incident and their distaste for an earlier Yahoo Mail redesign. One reader specifically claimed the outage disrupted his work on a "complex legal matter," saying it had effectively taken away his access to necessary documents.

While Mayer says Yahoo Mail's "uptime" is at 99.9 percent, even with this incident, in the Internet age that may not be good enough.