Service has been restored to Blackberry users after an overnight failure caused the system to be unable to send e-mails. Research In Motion said the exact cause of the problem is still unknown.

North American users were affected by the problem, said to have begun around 5pm Eastern on Tuesday. Service began to come back around 4am Eastern, although problems associated with the backlog of e-mails may still result.

"Root cause is currently under review," the company said in a statement to the press. "RIM is closely monitoring systems in order to maintain normal service levels." The problem did not affect the placing of voice calls.

Mails sent during the blackout may take awhile to be delivered, as the service gradually addresses the backlog. This is likely being done to prevent any bottlenecks or other service issues.

While messaging was the service most affected, some said Internet browsing was also malfunctioning. The Wall Street Journal reported that Blackberry users in outside of North America in London and Hong Kong were reporting problems as well.

Even with service restored, several carriers are still reporting customers complaining of service issues. A recorded message on the RIM Customer Support line advises customers that they are aware of the issues, however it provides no estimate as to the full restoration of service.