Yahoo CEO Marissa Mayer. AP Yahoo Mail has been down for some people since Monday.

Yahoo had previously said that it expected to have everything fixed by 3 p.m. PT yesterday. But that clearly didn't happen.

"@Kidsonthekorner Hi Beth, we're working on this right now and we expect all emails to be delivered by tomorrow afternoon," Yahoo Mail recently tweeted.

Late last night, some forms of Yahoo Mail were restored, but the company is still working on a format called IMAP, which lets Yahoo Mail sync better with other email apps. At the time, Yahoo said the best way to access email on mobile is through the official Yahoo Mail app.