Research in Motion's ( RIMM) BlackBerry email service has plunged into darkness.

The company said in a message to users late Monday that it had a "critical severity outage" within its Americas network, according to Reuters. RIM didn't provide an expected timetable for when it expects to be functioning again.

RIM handles mobile email service for many companies and organizations in the U.S., and has about 9 million customers worldwide.

The last BlackBerry outage came in April, when service was disrupted for several hours.

RIM shares fell 58 cents to $93.89 in after-hours trading Monday.

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