Yeah I'm talking more about how every other mail provider has their own rules and you have to set it all up. Like one requires your mail domain to me an AAAA record (where I've used a CNAME) and other things.
That's not just one, most require AAAA or A records.
With SPF, DKIM, DMARC correctly set up, correct IPv4 and IPv6 reverse DNS, only A or AAAA or NS or GLUE records used in the entire resolution path, correct from and reply-to addresses, you should usually be good to go, though.