Hi David
I am assuming that you are mentioning about your webmail and not actual outlook client.If this is related to webmail, This is because of the new Office365 portal design change rollout that happened recently. You should see a red Grid icon to the left top corner of the webpage. Clicking on that will drop down all your apps. You can also pin them back to Nav bar as shown below. Please let me know if you need any more information in this regard. Thanks
