I have a complex Tailscale-based network setup that includes blocking all Google hostnames. Unfortunately RCS on iOS doesn’t work when sending photos.
I’ve scoured AT&T’s website and App Privacy Report on iOS (which doesn’t show DNS names for Messages, Phone apps) but I do know they switched to Google as their RCS provider at one point.
I’d like to set up a Tailscale App Connector using hostnames, but if they’re using IP addresses I can work with those as well (subnet routing).
Probably easier to just unblock Google, send some messages, then look at your filter logs to see where they are going.
Guarantee you’ll run into issues when you hop towers or networks though.