Outlook normally shows a ScreenTips when you hover the mouse pointer over a toolbar button. Here is how you can show or hide the ScreenTips:
In Outlook 2003 and 2007:
1. In the main Outlook window, click Tools > Customize…
2. Click the Options tab. look at the “Other” section at the bottom of the dialog box.
3. Tick the checkbox for “Show ScreenTips on Toolbar“. To hide the ScreenTips, simply untick the checkbox.
4.You can also tick the checkbox for “Show shortcut keys in ScreenTips” if you want to see the shortcuts as well.
5.Click Close to return to the main Outlook window.
In Outlook 2010:
1. In the main Outlook Window, click the File tab > Options…
2. In the General section, look under “User Interface Options“. For ScreenTip style, select “Show feature description in ScreenTips” from the drop-down as shown below.
3. Click Ok to return to the main Outlook window
If you now hover your mouse over one of the button, you will notice a ScreenTip appearing.