I’m aware most ISPs do not allow for port 25 to be open for email use outside of business licenses, but at what level is that controlled? Can I get around that by owning my own router? Owning my own modem or ONT? Or is this just a thing they mystically control further up the pipeline that a relative layman such as myself can’t get around?
The ISP is going to keep those important network security settings far away from its clients. Owning your own router or ONT will not let you change anything other than your internal network settings.