Does every single network client on your network use your DNS server for name resolution? No DNS-over-HTTPS? No widgets configured to talk to public DNS servers

Does every single network client on your network use your DNS server for name resolution? No DNS-over-HTTPS? No widgets configured to talk to public DNS servers? Also, does your DNS server correctly filter "out"-of-bailiwick responses for .lan etc. zones that are actually perfectly well in-bailiwick because they're from the actual delegated-by-the-real-root-servers nameservers, they're just not from your private server that you've configured? If not, I can execute a cache-poisoning attack against you.