The company behind the BlackBerry smart phones said a three-hour e-mail outage Monday was caused by an upgrade designed to increase capacity.
Research in Motion Ltd. said Tuesday that the upgrade was part of "routine and ongoing efforts," and that similar upgrades in the past had caused no problems.
The outage, which started about 12:30 p.m. PST, annoyed subscribers who are used to checking and writing e-mail whenever they're in cellular coverage and able to make voice calls. It affected only some of the BlackBerry users in North America -- for others, the service kept working fully.
It was the second major outage for the service in less than a year. In April, a minor software upgrade crashed the system for all users. A smaller disruption in September also was caused by a software glitch.
Research in Motion, which is based in Waterloo, Canada, has been on a tear, adding 1.65 million subscriber accounts in the quarter ended Dec. 1, for a total of 12 million subscribers worldwide. It has deals with scores of wireless carriers around the world.
Experts said the company's system was relatively reliable, but its centralized structure meant that when there were problems, they could affect millions of users.
E-mail sent to and from BlackBerry phones in North America all goes through a Network Operations Center. It appears that the problem occurred there, when one of two Internet addresses that relay e-mail from corporate servers stopped responding, said Zenprise, a Fremont, Calif., firm that helps companies troubleshoot BlackBerry problems.
"Any time you got a system that's got a NOC, a Network Operations Center, you have the potential for a single point of failure," said Jack Gold, with technology analyst firm J.Gold Associates in Northborough, Mass.
"What's a bit surprising to me is that with all the work they've been doing over time . . . that they haven't been able to have enough redundancy in the NOC so that there isn't a single point of failure," said Gold, who has done business with Research in Motion.