Yahoo Mail 'being restored' following service problems
Some Yahoo Mail users have not been able to access their email since Monday following a service failure blamed on a hardware problem in one of its data centres.
The firm said that most accounts were now restored but warned of a backlog of emails still to be delivered.
Yahoo revamped its mail service in October, with the changes angering some users.
Since then it has had a series of problems with the service.
The latest of these began on Monday.
"We're very sorry for recent difficulties with Yahoo Mail, said Jeffrey Bonforte, senior vice president of communication products.
"The issue has been harder to fix than we originally expected."
An update from 07:15 GMT (23.15 PST) said that most affected accounts had been restored but that there was a backlog.
"The affected servers have been up and running for over six hours and we've already delivered over 30% of messages sent during the outage. We expect all emails to be delivered by tomorrow afternoon."
Some users claimed that issues with the service spanned back at least two and a half weeks.
Yahoo Mail has had something of a rollercoaster ride since it was redesigned in October.
Thousands of users complained at the removal of key functions and others reported technical problems.
These includes the removal of tabs, meaning users could not organise their inboxes. Other complained about the placing of the delete button next to the sender name and no longer having new emails in bold. Some reported that emails were disappearing from their folder after sending.
Then a leaked email from Mr Bonforte revealed that only a quarter of Yahoo employees had switched from Microsoft Outlook to the new-look Yahoo Mail, despite edicts from the management team to do so.
"It's time for the remaining 75% to make the switch," he urged.