You don't need to keep Outlook 2013 maximized on screen at all times to see when a new email arrives. As long as the program is running in the background, you can receive a notification at any time alerting you of the arrival of new mail. To set up this feature, you must change Outlook's settings.
Turn on Notifications
Outlook offers several notification choices in the Mail section of the Outlook Options window. To access this area, click "File," select "Options" and then select "Mail." Scroll down to the Message Arrival section, click the checkbox next to the type of notification you want -- "Play a Sound," "Briefly Change the Mouse Pointer," "Show an Envelope in the Taskbar" or "Display a Desktop Alert" -- and click "OK."
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Change Notification Sound
If you decide to use a sound notification, you can select one that matches your preferences. Close Outlook, go to the Start menu, select "Control Panel," click "Hardware and Sound," click "Sound" and select the "Sounds" tab. Make certain the Sound Scheme shows "Windows Default" and then, in the Program Events box, locate and select "New Mail Notification." You can choose an existing sound on the Sounds menu or click "Browse" and find and select a WAV format sound file. When you're finished, click "OK" and reopen Outlook.