Microsoft is working on adding SMTP MTA Strict Transport Security (MTA-STS) support to Exchange Online. The company is also working on including support for the DNSSEC (DNS-based Authentication of Named Entities) and DANE for SMTP. Support for the two SMTP security standards will be added to both inbound and outbound mail, “specific to SMTP traffic between SMTP gateways”” Microsoft is planning to make it generally available in December in all environments for Exchange Online users.”
Source: https://www.bleepingcomputer.com/news/security/office-365-adds-protection-against-downgrade-and-mitm-attacks/