Apple traffic goes to 17.0.0.0/8 + CDNs aliased to .apple.com, which my egress router blocks except for Apple-documented endpoints for notifications and software update, https://support.apple.com/en-us/101555

appldnld.apple.com configuration.apple.com gdmf.apple.com gg.apple.com gs.apple.com ig.apple.com mesu.apple.com mesu.apple.com ns.itunes.apple.com oscdn.apple.com osrecovery.apple.com skl.apple.com swcdn.apple.com swdist.apple.com swdownload.apple.com swscan.apple.com updates.cdn-apple.com updates-http.cdn-apple.com xp.apple.com

There was no overlap between unexpected traffic and Apple CDN vendors.