Exchange RFC 6710, RFC 6758 and RFC 4021 compliance

I need to verify whether Exchange Online supports the following SMTP extension RFCs:

RFC 6710 - Simple Mail Transfer Protocol Extension for Message Transfer Priorities (MT-PRIORITY)

RFC 6758 - Tunneling Plaintext Authentication Credentials Using TLS (CRAM)

RFC 4021 - Registration of Mail and MIME Header Field Names

Specifically, I need to know:

Are these RFCs implemented and advertised in the Exchange Online SMTP EHLO response?

Is there official Microsoft documentation that lists the complete set of supported SMTP extensions for Exchange Online?

If these RFCs are not supported, is there a published list of unsupported RFCs or a roadmap for future implementation?

Context:

I'm integrating third-party mail systems that require RFC 6710 (MT-PRIORITY) support for priority message handling. Currently, Microsoft documentation only references RFCs 3030, 2920, 6698, and 8461 as supported extensions, but there is no comprehensive list of unsupported RFCs.

Any clarification or documentation would be greatly appreciated.