The primary purpose of Conditional Access is to prevent company accounts from being accessed on personal devices. However, Conditional Access cannot prevent other company accounts from being accessed on company devices.
Of course, if a company device can access Naver Mail and Google Drive, it means the company is not very concerned about data leakage, and you may disregard this post.
To use M365, you need to open MS-related URLs such as office.com. Tenant Restriction is a concept used to prevent access with other company or personal accounts (such as outlook.com) during this time.
The Policy ID is generated as shown below. Make sure to copy each value and keep them.
To set up a blocking policy for external accounts, configure it as shown below (default settings).
To block all external apps, configure the settings as shown below.
Step 2: Enable tenant restrictions on Windows managed devices (preview)
In the technical documentation, there are guidelines as shown below.
Tenant restrictions V2 on Windows is a partial solution that protects the authentication and data planes for some scenarios. It works on managed Windows devices and does not protect .NET stack, Chrome, or Firefox. The Windows solution provides a temporary solution until general availability of Universal tenant restrictions in Microsoft Entra Global Secure Access (preview).
-> Although the content is difficult to understand, it can be interpreted as indicating that the feature will be provided in a different way in the future. Currently, it is in the preview stage.
Download the ADMX files for the latest Windows GPO policies.
Once installed, the policy files will be saved to the following location.
Depending on the method of policy deployment in AD, copy the PolicyDefinitions folder to the appropriate location with only the necessary languages. (This part of the policy is related to AD, so we will not cover it here.)
Run gpmc.msc on the Domain Controller (DC).
Create a policy in the Organizational Unit (OU) that you will use for testing. Right-click and select "Edit".
There has always been a need to synchronize address books (GAL) between companies in scenarios such as M&A, affiliated companies, or group companies, where using a single tenant is not possible. Traditionally, this was achieved by setting up servers like Microsoft Identity Manager (MIM) on an On-Premise Exchange Server, creating objects between ADs to synchronize address books. Alternatively, it could be implemented through HR integration solutions.
However, adopting MIM or HR integration solutions can be prohibitively expensive and requires specialized knowledge for management, making it very burdensome.
Recently, it has become possible to synchronize address books with Cross-tenant Synchronization. Specifically, this functionality automates the invitation of Guests.
Step 3: Automatically redeem invitations in the target tenant
Trust settings > Automatically redeem invitations with the tenant [Tenant Name] > Check > Save
Step 4: Automatically redeem invitations in the source tenant
Entra Admin Center > External Identities > Cross-tenant access settings
Add organization
Enter Target Tenant ID > Add
Outbound access > Inherited from default
Trust settings > Automatically redeem invitations with the tenant Fabrikam > Check > Save
Step 5: Create a configuration in the source tenant
Cross-tenant synchronization
Configurations > New configuration
Specify the configuration name. > Create
Step 6: Test the connection to the target tenant
Get started
Provisioning Mode: Automatic > Admin Credentials > Tenant Id: Target Tenant ID > Test Connection > Save
Step 7: Define who is in scope for provisioning (Source Tenant)
Provisioning > Settings > Confirm Scope > Sync only assinged users and groups:
This means specifying only certain users or groups to synchronize.
Users and groups-> Add user/group
None Selected
Specify the target. > Select > Assign
Step 9: Review attribute mappings
If, for various reasons, you do not want to synchronize specific attributes, proceed as follows.
Provisioning > Mappings > Provision Microsoft Entra ID Users
You can remove some items except for the required fields.
Step 10: Start the provisioning job
Start provisioning
Target Tenant > Entra admin center > Users > All Users
You can verify that they are added as guests as shown below.
You can also verify this in the Exchange Admin Center as shown below.
You can also verify this in the address book as shown below.
Tenant-to-tenant synchronization settings are configured as follows: In the Source Tenant, set up the Outbound settings, and in the Target Tenant, set up the Inbound settings. This synchronization process results in Guest accounts. Since Guest accounts have Mail User attributes, they can be verified in the address book.
