1. Visit https://protection.office.com/quarantine and login.
2. Select "Threat Management" and then "Review".
3. Select Quarantine.
4. Select the quarantined message from the list, you can click "Preview message" to view it before releasing it.
5. To release the message, select the "Release message" button, and then click "Release Message".
Once released, the email will show up in your mailbox within a couple of minutes.