Microsoft hopes to accelerate the removal of TLS 1.0 and 1.2 connections from Exchange Online by disabling connectivity in 2022 and forcing organizations which need to use the older protocols to connect to a new “legacy smtp” endpoint. It’s not a bad plan because it transfers responsibility for choosing to use obsolete connections to customers. Most organizations will go with the flow (no pun intended) and use TLS 1.2, but those who need some time to update applications and devices know what they have to do.
Exchange Online now insists on TLS 1.2 connections between email clients and servers. PowerShell scripts using the Send-MailMessage cmdlet will fail. The problem is easily solved by forcing PowerShell to use TLS 1.2 to connect, but it does mean that some work is needed to check scripts (before they fail).