It sounds like you're asking for [MTA-STS](https://dmarcian.com/mta-sts/)
"MTA-STS is an inbound mail protocol designed to add a layer of encryption/security between sending and receiving mail servers."(..)
"The MTA-STS protocol works by having a DNS record that tells mail servers to fetch a policy file via HTTPS from a defined subdomain. This file contains a list of the receiver’s mail servers which are authenticated and approved to receive the messages and also what policy to apply to inbound messages."