Research in Motion said today that BlackBerry service has been restored after a network failure caused a blackout of its push e-mail service throughout North America last night.

The outage, which occurred at about 8 PM ET, lasted throughout the night with intermittent service restored in the evening and this morning, but full service wasn’t restored until this afternoon. RIM didn’t give a reason for the service interruption.

"Root cause is currently under review, but service for most customers was restored overnight, and RIM is closely monitoring systems in order to maintain normal service levels,” RIM said in a statement.

RIM is keeping generally quiet about the service interruption. It notified its customers about the problem this morning, but it has provided no information about the service outage on its Web site and has issued only statements to the media, and its customer support number carried a message reporting “technical difficulties” on the network.

There are about 8 million BlackBerry users globally, but not all were affected by the service problems.