Whenever you receive a new email, Outlook 2010 displays a desktop alert. If you wish then you can also disable this desktop alert. But it is useful in many cases, lets see how we can change the default settings of new email alert.
Click the File (Office) button and choose the Options and them navigate to the Mail option in the left side column and click the Desktop Alert Settings button under the Message Arrival section.
The Desktop Alerts Settings dialogue box will be displayed, now make changes to the new email message settings like Duration and Transparency by moving the slider and adjusting the values you feel suitable. Duration specifies the time new email alert stays on the desktop.