Interesting discussion - thank you.
I only use POP3 for my 6 email addresses. On my main PC I download everything and set the classic Outlook client to delete it fron the server after 14 days and unless it's junk keep it locally, forever. I back up my PST files to a remote NAS box.
I also download emails to my android phone using Samsung Mail every 15 mins and only keep live ones.
I have email pop3 clients on a couple of other machines and download emails to them when I need to. I can go back xx days
So I have virtually nothing left on my ISPs system. And local copies of everything on my LAN.
My wife has her own POP3 email address on my domain and uses her own POP3 client to keep her stuff separate and reasonably private.
I also use MyPhoneExplorer to sync my classic outlook contacts and calendar with my Android phone and vice versa.