I have now run into this issue several times when sending mail when Private Relay is turned on. My mail is bounced by the receiving mail system because it is coming from an IP address associated with spam and fraud, I can sometimes just re-send and Apple uses a different IP address and the mail goes through. I just wonder where Apple is finding these IP addresses - perhaps those abandoned because they only sent spam and fraud email. The only other noticeable consequence of Private Relay is web sites that think I live in Los Angeles (I’m really in Las Vegas) - obvious in the advertising that I see. I particularly like the link “If you live in these zip codes….” when the zip codes are all California!
They could be IP addresses assigned to a block of cloud servers.
I’ve read about brain-dead mail filters blocking the entirety of Amazon Web Services because some spammer set up a bot there. Even though Amazon shut down the account a few days later, that’s sometimes enough to convince some mail-filtering companies to install permanent bans on the entire IP address block.
As for location tracking, using IP addresses for geolocation is frequently nonsense. I frequently find web sites thinking that I live 30 miles to the east of my actual location, because that’s the Comcast central office where my IP address block is registered.