I have two laptops. Let's call the laptop described above as Laptop A and the other one as Laptop B.
Laptop B has Outlook 365 (16.0.12527.20260) 32-bit on it. It's been pretty much rock solid - not only does it have the two accounts mentioned above in it, there's a 3rd account in there, also a SmarterMail account, also using MAPI. For quite some time it's been running with no issues with any of the accounts.
So in order to reset Laptop A - delete the Outlook Profile, remove the "connections" within SmarterMail, and re-setup, I paid particularly close attention to the Connections page within SmarterMail. Here's a screenshot of what it looks like there:
The iPad and iPhone connected using EAS have worked absolutely flawlessly for several months - kudos to the team for getting those to work perfectly as designed.
Whenever I do a reset on Laptop A - I will go into this page in SmarterMail and I will delete the "Outlook (MAPI)" device and the "EWS (EWS)" device. I'm not sure which one is which, so I usually just delete both of them.
So this time, I deleted both of those again, and then before setting up the account on Laptop A, I opened Outlook on Laptop B to see what got created in the list again - and it created the "Outlook (MAPI)" one.
Then I created the account in Outlook on Laptop A, setting it up as an Exchange account - and using Fiddler shows that it's using MAPI - but that's when the "EWS (EWS)" device showed up in the list.
I figured that there should be two MAPI devices listed but there were not, and I'm not sure why the EWS account was showing up. So then what I did was close Outlook n Laptop A, turn off Laptop B completely, delete both the "Outlook (MAPI)" and the "EWS (EWS)" devices from the list of Synchronized Devices, then open Outlook on Laptop A again.
This then re-created the "Outlook (MAPI)" account pretty much immediately, and then eventually it re-created the "EWS (EWS)" account as well.
This raises a whole host of questions...
1) Why when there are two different devices which are connecting using MAPI, is there only one device listed in the Synchronized Devices list?
2) Why is Laptop A creating an EWS connection?