Re: Disable viewing Groups in Outlook (Web and Desktop)

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Deleted wrote:
I don’t think that’s what it means. All that does is hide it from the address list by default. The groups will still show in outlook.

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Nope. The HiddenFromAddressListsEnabled flag hides a group (or another mail-enabled recipient) from Exchange Online address lists. The HidefromExchangeClients flag is completely different and prevents Exchange clients (OWA and Outlook) even realizing that groups marked with this flag exist. https://www.petri.com/hiding-office-365-groups-exchange-clients

As to hiding the Groups root, I don't think this is possible even when someone belongs to zero groups.