In fairness, we were putting out articles and blogs around January and February of 2022 to let partners and customers know that O365/EXO was going to deprecate basic auth and it would impact Exchange emailing, in order to get as many customers upgraded and on that functionality as possible before the Oct 2022 deadline.
To be brutally honest, Microsoft's GP implementation of Modern email authentication has been far from ideal.
Its only very recently in the latest GP 18.4 build and now 18.5 builds that MFA implementation is workable. Leaving a very short window for the customer base to upgrade. 18.3 and 18.4 builds had numerous issues, including attachments size and string limitations, token timeouts, AUS client totally broken in 18.4 and then don't get me started on Workflow and workflow notifications, all having major issues throughout 18.4 builds.
In effect, it's really only very recently that customers can update to a stable GP build that works properly with Modern authentication. I have had customers have to update 2-3 times over the last year to try and fix up issues once they enabled modern email auth in GP. let's hope we have seen the last of the shortcuts Microsoft have been taking with the modern email implementation for GP, and its functionality and usability is bedded down and enhanced moving forward.
