> When sending mail to a mailbox at a subdomain, compliant senders MUST NOT attempt to fetch a policy from the parent zone. Thus, for mail sent to "user@mail.e

> When sending mail to a mailbox at a subdomain, compliant senders MUST NOT attempt to fetch a policy from the parent zone. Thus, for mail sent to "user@mail.example.com", the policy can be fetched only from "mail.example.com", not "example.com".[0] That's not great for those of us who like to use Fastmail's anything@user.example.com feature. This specification also doesn't work well for those who run their own SMTP servers and who are less likely to have cached policies. Meanwhile, the big email providers could hard-code a list of the other big email providers and never downgrade when talking to them (as I imagine they already do). So who's this spec for, then? 0. https://tools.ietf.org/html/rfc8461#section-3.4 https://tools.ietf.org/html/rfc8461#section-3.4