Yahoo's Mail service remains down for some users a day after the company said access would be restored.
The problem began affecting users Monday night, due to a hardware problem in one of its mail data centers, said Jeffrey Bonforte, senior VP of communication products, in a statement recently posted on Tumblr.
Yahoo first acknowledged the outage early Tuesday afternoon Eastern time in a post on its Facebook page, as well as on Twitter. Yahoo said it was aiming to restore access within the next few hours after those posts, but as of Wednesday morning Mail was still down for some people.
"The issue has been harder to fix than we originally expected," Bonforte said. Dozens of the company's employees are working to get the problem fixed by 6 p.m. Eastern time, he said.
The number of people affected by the outage is not clear and a Yahoo spokeswoman declined to comment further. But it could be on the order of multiple hundreds, if not somewhere in the thousands, judging from the level of activity in Yahoo's Mail forum.
The problem could have widespread implications on people's ability to communicate and get work done, given Yahoo Mail's prominence. With more than 100 million daily users, Mail is one of Yahoo's most important products.
In the forum, the discussion thread for the outage had more than 1,200 votes on it as midafternoon Wednesday Eastern time, with more than 500 comments from users. A smaller number of people appear to have taken to Twitter to express their frustrations.
For some of these people, their access to Mail has been down for two to three days.
Yahoo also has sent mixed messages about the outage. When trying to log in to Mail, some users have seen a page telling them that "scheduled maintenance" is taking place.
"I don't believe for one minute this is a scheduled maintenance thing," one person wrote in the forum. "They have been hacked and just don't want people to know what's going on."
Another person offered more practical advice. "People relax. It's not life or death. Have another email account, like Hotmail or Gmail," he said.
Yahoo has had a bit of a rough time with its Mail service lately. It was redesigned in October with a new Gmail-like interface, but since then some people have complained about the way that it looks, or how it functions.
Yahoo has even had challenges getting its own employees to use it, according to a recent report in AllThingsD.
Yahoo CEO Marissa Mayer has said that Mail is one of the top things she wants to improve to attract new users to Yahoo.
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