To ensure that content on Microsoft SharePoint Online sites can be shared only with new and existing guest users, you need to limit the external sharing settings in the SharePoint admin center. Here are the steps to follow:

Sign in to the SharePoint admin center with your admin credentials.

Go to  Policies   >   Sharing .

Under  External sharing , drag the  SharePoint  slider down to  New and existing guests . (The  OneDrive  slider is dependent on SharePoint and will also be set to  New and existing guests .)

Under  More external sharing settings , check the box  Allow only users in specific security groups to share externally  and select  Manage security groups .

Add the security groups that contain the users who are allowed to share content with guest users. You can also create a new security group if needed.

Click  Save  to apply the settings.

To prevent incoming Teams call notifications when users are already on a Teams call or in a Teams meeting, you can use the Teams admin center to enable the Mute notifications during meetings and calls option. This option will suppress the incoming call notifications without rejecting the call. The caller will still hear the ringing tone and the callee can still answer the call from the Teams app or the taskbar. Here are the steps to enable this option:

Sign in to the Teams admin center with your Microsoft 365 username and password 1 .

In the left navigation, go to Teams > Teams update policies.

Select an existing policy or create a new one by clicking Add.

In the Update policy pane, under Meetings and calls, turn on the toggle for Mute notifications during meetings and calls.

Click Save and then Close.

Note: You can assign different update policies to different users or groups of users. For more information, see Manage update policies in Microsoft Teams 2 .

To ensure that all unused teams expire and are deleted automatically, you need to configure a Microsoft 365 group expiration policy. This policy applies to teams because they are backed by groups. Here are the steps to follow:

Sign in to the Microsoft 365 admin center with your admin credentials.

Go to  Groups   >   Expiration .

Turn on the  Enable expiration  toggle.

In the  Group lifetime  box, enter  365  days or select it from the drop-down list. This means that the teams will expire 365 days from their creation date.

In the  Select group types to apply the policy  section, check the  Teams  box. You can also select other group types if you want.

In the  Choose how to handle owners of groups without owners  section, enter  adminLOD-Se551723.onmicrosoft.com  as the email address to receive notifications for the expiration of orphaned teams. You can also add more email addresses if you want.

Click  Save  to apply the policy.

That’s it. You have successfully configured a group expiration policy for teams. This policy will automatically delete the teams that are not renewed by their owners before the expiration date. You can also view and restore the deleted teams within 30 days from the  Deleted groups  page in the admin center.

Create information barrier segments first, then create information barrier policy based on the segments then start the information barrier application.

Microsoft Teams admin center > Org-wide settings > Guest access > Make private calls = off.