and the spam lists sledgehammer. A simple user will not know how to deal correctly with those spam lists (spamhaus, barracuda etc).
Also the ISPs are mostly clueless how to assign correctly a PTR record (reverse DNS) to an IP they already sell you. Is a mess, you must fight through hundreds of support calls until you get to the final boss that understand what you need for your own hosted email server.

I think nostr will replace email soon. Email as we know it is almost dead.