Microsoft Customer Service and Support, Lync/OCS and Windows Live Messenger teams are currently investigating a possible loss of service for enterprise Lync and OCS customers who federate with Windows Live Messenger. The appropriate teams are actively investigating this issue and are working towards the quickest possible resolution. I will update this notification again when full service has been restored or as developments warrant.
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RESOLVED: MSN PIC connectivity has been restored. Users may need to sign out and back into their client before seeing successful conversations/presence. Apologies for the inconvenience.