If your organization has an Exchange Hybrid deployment that is not running on Exchange 2013 SP1 or later you may want pay attention. On September 23, 2014, Microsoft will be making a certificate change to the Microsoft Federation Gateway which could affect you.

This change could also impact those who are sharing free/busy information between two different on-premises organizations. If you are already running Exchange 2013 SP1 then you are in luck as this task will be automated for you and you are not required to take any action. For those using older versions of Exchange, it is very important that you update your Federation Trust as failing to do so will result in loss of free/busy and mailtip functionality. Microsoft released the following post that provides more information as well as the recommended actions that should be taken, I strongly recommend paying attention to this if you are not on the latest version of Exchange 2013.