Microsoft
Microsoft
We have had issues with Autodiscover in this same configuration and the registry key you are thinking of is ExcludeExplicitO365Endpoint and value of 1 as described in this intermedia KB, https://kb.intermedia.net/Article/39713. I expect this registry key may also mitigate the current search issue too.
To fully address the issue and not need the registry key or other mitigations we need to separate the MSA account from the work email addresses. My understanding of the way to do this is to create another Alias on this page, https://account.live.com/names/Manage. Then use that alias to sign into Office. The Outlook Team would say to remove the work email address from the MSA alias list. And, maybe that will be the case. However, I would like to see if you or someone else here could test creating a new alias and then use that to sign into Office if it mitigates search.
What else may be needed:
1. Does the new MSA alias need to be Primary alias? I am not sure and we will need to try it if the new secondary alias by itself is not sufficient.
2. Is it necessary to remove the work email address from the MSA alias list? This may also be needed but would prefer to not remove it unless it becomes necessary.
On the page I linked above this is how it looks to add a new email alias.