The problem persisted, however, and on June 6 Knight wrote that, despite the fix, outstanding issues remained and that Yahoo would continue seeking a solution.

He also explained the new features whose rollout led to the problems: "Recently we made some changes to how external account retrieval works. Most notably we added SSL functionality (enhanced security technology), which many users have been clamoring for. We are also taking steps to improve spam blocking for messages that are being retrieved from these external accounts, by running them through more aggressive filters. Unfortunately we encountered some unexpected problems that lead to server errors or processes timing out for some users," he wrote.

On Tuesday afternoon Yahoo spokeswoman Kelley Podboy confirmed that Monday's blog posting from Knight contained the most recent information available about the issue. "We are also sending direct e-mail to all users who have recently enabled SSL external accounts to notify them of the change," Podboy said via e-mail.

Yahoo Mail has two POP-related services, according to Podboy. One is "POP in," a free service for retrieving messages from external accounts, which is the one affected. Another is "POP out," for downloading messages using a desktop e-mail application, such as Outlook, and accessing them offline. The latter service is unaffected by the problem and available as a premium feature to Yahoo Mail users who pay US$19.99 per year for the service's "Plus" plan, she said. Both services are available to users of Yahoo Mail Classic and the New Yahoo Mail.

Another Web giant faced technical problems in recent days: Amazon's main site had availability and performance problems on Friday and Monday.