It does look like they are actually for clients (i.e. MUAs doing IMAP & Submission), not for relay (i.e. MTAs doing SMTP/SMTPS).
I've used MTA-STS and XML to enable auto-config for my stuff:
https://vadosware.io/post/thunderbird-autoconfig-for-your-se...
Oh and it looks like MTA-STS might be the solution:
https://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocol#...
Turns out there's an excellent guide by the UK government:
https://www.ncsc.gov.uk/collection/email-security-and-anti-s...
https://www.security.gov.uk/guidance/email-guidance/mta-sts/...
Relevant RFC:
https://datatracker.ietf.org/doc/html/rfc8461
It does look like they are actually for clients (i.e. MUAs doing IMAP & Submission), not for relay (i.e. MTAs doing SMTP/SMTPS).
I've used MTA-STS and XML to enable auto-config for my stuff:
https://vadosware.io/post/thunderbird-autoconfig-for-your-se...
Oh and it looks like MTA-STS might be the solution:
https://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocol#...
Turns out there's an excellent guide by the UK government:
https://www.ncsc.gov.uk/collection/email-security-and-anti-s...
https://www.security.gov.uk/guidance/email-guidance/mta-sts/...
Relevant RFC:
https://datatracker.ietf.org/doc/html/rfc8461