Ingress - out of the box rspamd is pretty decent and it is rather configurable.
Egress - DNS (A,AAAA, PTR), (E)HELO, SPF, DKIM, DMARC. "IP Reputation".
There are absolutely no shortcuts and yet most of the problems I diagnose regarding email delivery will find a missing PTR record or a miss-configured (or non configured) HELO. You cannot be lazy when it comes to email. SPF + A + AAAA + PTR and (E)HELO is a minimum.
There is one thing that you cannot generally, personally mitigate and that is being on a deny list due to your IP address. This one is a bit more tricky to deal with. You might have to use a relay. Another mitigation might involve IPv6.