While most customers and partners will receive this information via their account teams, I am sharing for broader reach.
We are updating the way our customers/partners federate with Microsoft.
Prior to the change on Friday, October 2, 2015 at 8:00 PM PDT, customers need to update their federation using URL filtering.
If you or your customers “hard-code their IP addresses,” they will need to allow IP: 188.8.131.52 to ensure there is no interruption to their federation with us.
Going forward, please use “URL filtering” on sipfed.microsoft.com, which means you won’t need to update your IP addresses when Microsoft makes a change anymore!