How to set the number of days spam emails must be quarantined in Office 365?

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

Step 2: Navigate to Exchange admin center.

Step 3: On the left pane, scroll down and click More features.

Step 4: Click open under Permissions.

Step 5: Click Protection on the left pane.

Step 6: Switch to the spam filter tab.

Step 7: Double-click on the default policy.

Step 8: Click on spam and bulk actions.

Step 9: Under the quarantine section, in the Retain spam for (days): box, enter the number of days and click Save.