Exchange Online Launches Support for MTA-STS
Exchange Online now supports SMTP Strict Transport Security (MTA-STS), a mechanism to help defend SMTP communications between mail servers. Microsoft 365 tenants can decide if they want to enable MTA-STS for their domain by publishing a DNS record and an MTA-STS policy. You don't have to use MTA-STS, but it's a good idea to consider the option.
February 4, 2022