Reference my original blog on an Additional Windows Live Messenger PIC/Federation IP Address
Tomorrow’s planned added capacity has been postponed for technical reasons and to provide additional time for administrators to update their firewall settings if necessary to reflect the additional IP address. The new date that this work is scheduled to go into place is Friday, March 26, 2010. For organizations that have chosen to restrict this traffic to specific IP addresses, you must have the list in KB 897567 in place prior to Friday, March 26, 2010 or PIC connectivity with MSN will fail.
897567 Known issues that occur with public instant messaging and Communications Server
I will provide reminder notifications as the date approaches.