It is still difficult to be certain of how you have set up your Android email, Martin_Williams.
Let’s assume that the Android is actually sending the email directly (via SMTP), rather than indirectly (by using SMTP to another, non-Microsoft email server, to relay to your Microsoft Exchange server), to your Microsoft Exchange server.
It is also quite possible that Google hasn’t, yet, made the protocol changes for the latest Internet email standards.
However, even if that is the case, it is highly likely that Google will make that change before Microsoft does.
At which time, you’ll simply be back in the same issue.
This is, basically, what you, and anyone, can expect from just about any workaround, so long as the root cause (Microsoft Outlook and Exchange) is not fixed.
In addition, as has been explained by others (as well as myself), any time one uses a tool for something other than its intended purpose, one is perpetrating a workaround, and is subjecting themselves to the all too usual vagaries of any workaround: it will breakdown, sooner or later.
It happens because things will be changed in order to better serve the intended purposes, without consideration of those “side” uses that are using the system for a workaround for other intended purposes.
The very best long-term strategy is to do your “homework”, and find tools that better match what you are actually trying to accomplish, rather than simply continuing to use a tool that is intended for an increasingly divergent purpose, simply because that old tool is familiar.
However, you are certainly free to choose to do whatever you wish.