Show or hide enhanced ScreenTips
    Outlook
    
      2016
      
    
  
  
  
  
  
    By default, Outlook shows document tooltips (or screentips) when you hover on a button, but this option can
            be turned off.
  
  To do this, follow next steps:
1. On the File tab, click the Options button:
            2. In the Outlook Options dialog box, on the General tab click the ScreenTip Style drop-down arrow, and choose one of the following settings:
            - Show Feature Descriptions In ScreenTips to display larger ScreenTips with the tool button name and an explanation of its function.
 - Don't Show Feature Descriptions In ScreenTips to display only the tool button name.
 - Don't Show ScreenTips to display neither enhanced nor standard ScreenTips.
 
3. Click OK.
See also this tip in French: Afficher ou masquer des info-bulles.