Effective spam filtering need lots of spam
I figure you need about 500,000 spam messages a month to be able to filter it out properly while minimal false positives. That means you have to be able to throw out about 10 gig a month of data over your home network. It is easy to collect that much if you just put in some random email address in a web page but the spammers will throw away the ones that look randmon like email@example.com but firstname.lastname@example.org will get far more spam. Common names all get spam as well so alice, bob and smith will get spam very soon after starting up a new server.
There are antispam services that you point your MX records to and they do the filtering and then deliver to your home server. They can install SSL certs so they only deliver to your dynamic IP address and some can do IPv6 which you might find is static. I have a computer in a data center in LAX and I've about given up on trying to filter spam and letting others try. I'm currently using MXGuardian which seems to work but is getting expensive as I keep finding more and more email address I set up years ago that are still being used. Most of the services are cost per doamin, cost per mailbox or cost per message. With over 100 people using my vanity domain over the last two decades, any of those options get expensive. My habbit of using a new email address everytime I print business cards just adds to the expense.