A technical problem with Yahoo Mail left one in five of its users out in the cold for several hours Wednesday.
The problem manifested itself as both slower service and denied access for some users, said Katie Burke, senior producer of Yahoo Mail, a free email service based on Four11's Rocketmail, which Yahoo (YHOO) acquired last year.
Burke said email service had been fully restored by Wednesday afternoon, and no email messages were lost. Undeliverable messages were queued for later delivery.
"We're in the process right now of delivering all the mail that's been queued, which will resolve with a couple of hours delay," Burke said.
Stephen Grubb, a corporate trainer for a long-distance company based in Carmel, Indiana, said his service went down between 4 and 5 on Tuesday afternoon, was restored later that night, and failed again Wednesday morning.
"I rely on Yahoo Mail for personal sites that I publish.... It's great when it works," Grubb said.
The company did not disclose the origin of the problem, but Burke confirmed that it was unrelated to any other Yahoo feature, including its newly released Yahoo Calendar, an email-based reminder service.
Cindi Bennett, marketing and communications director for high-performance email service providers Critical Path, said such outages were usually a result of the architecture used by email providers.
"It's one thing to be scalable at one domain, and that can take you anywhere from one user up to, reasonably, a couple million users," said Bennett. "The problem is that what you're really doing in a situation like that is probably not scaling. It's probably replicating, which means that every time you add a large cache of new users, you need to replicate onto another server."
If around 20 percent of a system's users are affected, she said, it has to be tied to a particular server.
"Why is 20 percent of Yahoo Mail's customer base unable to access email right now?" Bennett said. "Probably, those 20 percent of users all have a server in common, and what's happened is that server is having problems, so that everybody from letter A to D, let's say -- who are resident on that server -- don't have accessibility."
There are more than 18 million registered users of the various Yahoo services, but the company did not disclose the number of users to its Yahoo Mail service, which launched in October 1997.
