You can choose which actions will appear at the top corner of your message when you select a message to read, as well as those that will appear on the message toolbar when you’re composing a message. You can add many actions, or just a few.
Some actions are selected by default, but you can clear them if you prefer.
At the top of the page, select Settings > View all Outlook settings.
Select Mail > Customize actions.
Choose actions to appear at the top of your message
To choose which actions appear at the top corner of your message when you read or reply to email:
Select the check boxes for the actions you want. They’ll appear at the top corner as you select them.
To change the order in which they appear, select them in a different order.