Hi @J MacGillivray ,
In the past we used a shared Outlook Public folder for this purpose which automatically synchronized with our phones. (Android native Contacts app)
By "shared Outlook Public folder", are you referring to the shared Outlook contacts folder introduced in this article?
Do you mean this has been working flawlessly in the past but suddenly does not work anymore?
Could you provide more details about the issue symptom, like is there any error message when users fail to access the shared contacts folder.
From the perspective of Exchange server and Outlook desktop client, I'd suggest trying to double confirming if the folder permission of the shared contacts folder has been set properly. Or you can test by creating a new contact folder and see if it can be shared and synchronized as expected.
Besides, since the "Outlook" tag is just for general questions related to the Outlook desktop client so I am afraid I can hardly help regarding the issue on the Android native contacts app. Given this, you can try reaching out to the support for the Android mobile as well to see if they can shed some light on it.
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