Credit to Arvind Iyer on this post.
If after you have run the IdFix tool and verified that your Sync profiles have the msExchHideFromAddressLists attribute selected and still the check box in the Exchange Admin Center is not check. Pull your hair out, then follow these steps.
- Open the Synchronization Rules Editor on the Azure AD Sync server.
- Filter by or go to Inbound Rules, and find the “In from AD – User Common” rule and click Edit.
- Make sure it is not the User Common Microsoft Exchange rule.
- Select Transformations from the left navigation,
- Click, Add a Transformation as a Direct flow type, a Target Attribute of msExchHideFromAddressLists, and a source of msExchHideFromAddressLists.
- Then click Save and make sure to run a new sync to your 365 tenant.
Once the sync is completed you should begin to see in the Exchange Admin Center, the Hide from Address List box checked.
Have you ever encountered this? If so, let me know if this solution worked or if you found another method.