We are very sorry for recent difficulties with Yahoo Mail.
Some of our users have not been able to access their mail since 10:27 PM PST on Monday night, due to a hardware problem in one of our mail data centers. The issue has been harder to fix than we originally expected.
We have dozens of people working around the clock to bring it to a resolution. We believe our current efforts will restore our users’ access to their inboxes by 3 pm PST today. We’ll post again then on our @YahooMail Twitter handle.
by Jeffrey Bonforte, SVP of Communication Products
UPDATE: Please check our Help page for the latest information. (last updated on 12/18, 12:30 PM Pacific Time)