Well, I have finally given up on Microsoft. Their approach and attitude is unacceptable, and they certainly do not seem even remotely interested in customers like me. (There approach is simple, move to Microsoft 365, pay high monthly or annual costs per user for the whole 365 desktop suite (not just Exchange), and that's it, period.) It is a giant middle finger to customers. I have had enough. Zero movement from Microsoft, and in fact, that have had BACKWARDS movement over time, in that they keep clarifying their support for MS Office 2019 (which will now NOT be supported until the end of the LTSC (for big customers (not me, a little customer)) which goes beyond 2023, but MS will only support it with Exchange 365 until 2023 (next year.) You could not design a MORE CLEAR message from MS that Fixed cost (and static non-updateable systems, which are REQUIRED in some HIGH SECURITY SITUATIONS) are not supported AT ALL, PERIOD, the END.
https://www.consumersadvocate.org/hosted-exchange This link is nice summary of the myriad alternatives to MS 365 Exchange hosting. (About 1/3 of them are variations on MS 365 Exchange hosting, and one assumes those will be equally broken to MS's advertised limitations. But the other 2/3 of the offerings are for per user monthly subscription costs for hosted MS Exchange Server (not 365 Exchange) and various flavors of older Exchange: 2010, 2013, 2016, 2019, which do not have any of these new MS artificial requirements for clients. You can subscribe, and then use the clients that you want to use, free of Microsoft's cram downs that are for monetary purposes primary and "so called" security improvements a distant 2nd place. (That's just really the excuse, this is REALLY all about driving subscriptions to 365 Office desktop suite using 365 Exchange to force it. It is a pathetic money grab, and I am finally saying enough.) Good buy you useless greedy troglodytes.