For the second time in about a week, RIM is having a problems delivering emails to users of BlackBerry smartphones.

Details on this outage are sketchy, but it appears to have affected every BlackBerry user across N. America.

This is possible because of the way RIM's service is set up. All email messages sent to or from one of its devices go through a Network Operations Center (NOC), and if there's a problem with one or more of these, then email service is interrupted.

At this point, RIM has not given a public statement explaining today's outage. UPDATE: More details on this story are emerging, and the problem isn't as severe as first thought. According to a statement from RIM:
RIM did perform regularly scheduled maintenance on BlackBerry Internet Service that took longer than originally expected, and some BlackBerry Internet Service customers may have experienced slower delivery of e-mail earlier today. The majority of customers would not have seen any impact.
The typical BlackBerry Internet Service user is a consumer, rather than business users who generally use the BlackBerry Enterprise Server. This makes today's outage much less severe than last week's, which affected all users.
The company said last week's problem was caused by an "internal data routing system within the BlackBerry service infrastructure that had been recently upgraded." Ironically, the upgrade was intended to increase the speed at which emails are delivered.

Response from the Competition
In the wake of last Monday's outage, at least one of its competitors was quick to call attention to RIM's problems.
Palm, Inc. ran an ad in the New York Times last week that said, in part, "Palm Smartphones. They connect to your Microsoft Exchange Server. No third-party servers. No hassles. And more importantly, no nationwide blackouts."