How to apply a sharing policy to multiple mailboxes in Office 365?

Step 1: Sign into your Office account via https://portal.office.com/

Step 2: Navigate to Recipients > Mailboxes.

Step 3: Select the mailboxes to apply the policy.

Step 4: Scroll down and click More options.

Step 5: Click Update under Sharing Policy.

Step 6: Select the sharing policy from the list and click Save.