This has been a known thing on our end for some time.
This will essentially only impact those who use Microsoft online services, primarily Office 365, but we will need to update our migration tools by the time this takes effect.
The bigger concern, Microsoft is showing their hand for the future and it’s not the Microsoft we are all used to working with.
It started with delays to Exchange on-prem, talk about changing Exchange on-prem to subscription pricing (which they've backtracked on for now), their acquisition of Accompli and how communication is starting to move through Microsoft servers (e.g., "verifying" clicked links in Teams and Outlook). It culminates with a closed system where everything goes through their servers when using desktop or mobile Outlook’s, regardless of where you are hosting your email.
That said, not much will change on our end and EWS will still be supported in perpetuity.
But, in the very near future, we will be announcing methods for email users to enhance the reliability, security, and functionality not only to SmarterMail but clients you want to use with SmarterMail.
All these changes at Microsoft and Google, trying to prevent customers from accessing their data and in some ways making it extremely difficult to move from their services, make being in the mail server business a very good thing moving forward. We're actually looking forward to the implications of the decisions they're making.