Naively I thought that one value proposition of SPF, DKIM and DMARC is that reputation shifts from based on IP to be based on domain, once you set these up correctly. So as long as you can maintain a good reputation for your domain and have SPF, DKIM and DMARC correctly set up, then you can host your SMTP server at any IP and your emails will get delivered.
I wonder why it doesn't work this way.
IMHO, their main advantage is that third parties can’t send email which appears to originate from my domain.
I configure my domain to use SPF, so now spammers can’t sign it properly.
However, the fact that an email passes SPF verification only ensures that it was authorised by the domain owner. It doesn’t say anything about whether the domain owner is a spammer.
It does work like that except nobody actually knows Google or Microsoft's algorithms to allow or deny mail delivery. It's the whole SEO thing all over again.
It does work that way, but IP reputation is a thing as well so you need to keep that in mind. IPs need to be "seasoned" and "trusted" as well as domains.
This is how email-as-infra works, you're sending from a shared pool of their ips and they sign your emails with DKIM and you'll have SPF set up as well on your own.
Cause IP is a finite resource (even IPv6 where the granularity is more like /48) while domains are infinite.