There is a custom application defined "MSFT_Teams" which comprises of predefined apps - Microsoft Teams , Teams (Video) and Teams (Voice). What IP's/subnets are part of this custom Application?
Predefined apps like Microsoft Teams and Teams(Video) have a dynamically updating list of IP's managed directly by the vendor in this case Microsoft Corp. SSR does a real time lookup when a new session is formed to relate it to these predefined app's
More Information can be found herehttps://www.juniper.net/documentation/us/en/software/session-smart-router/docs/howto_ms365/
https://endpoints.office.com