Hide users disbaled users and shared mailboxes from GAL

[Fairtrade]

We are using Office 365 with AD sync.

I have a problem where I cannot hide shared mailboxes from the GAL...

The shared mailboxes where once users but after they leave have been converted to a Shared Mailbox.

I have set msExchHideFromAddressLists to TRUE on the AD side but still they are visible in the GAL (Even after 24hours)

I cannot set them hidden via the admin centre as i get the  failed because it's out of the current user's write scope error...

I can delete the AD object and it removes the users from the GAL but then it also removes the shared mailbox too.

Does anyone know a work arround? 

[#2]

Check whether the attribute change is picked up via the MIIS Client as detailed here: https://docs.microsoft.com/en-us/azure/active-directory/hybrid/tshoot-connect-object-not-syncing#con...

[#3]

@Fairtrade 

Please Check if the "mailNickname" attribute for the disabled users / shared mailbox is populated.

Another user attribute that must be populated for msExchHideFromAddressLists to work is the "mailNickname". Set this to their username. and run a delta sync. If this is not set, then msExchHideFromAddressLists doesn't work correctly. The GaL should update instantly on OWA.