You first want to create a Multi-KPI-Alert. You can read about that at http://docs.splunk.com/Documentation/ITSI/2.4.1/User/CreateMulti-KPIAlerts
Once you create the alert you can configure email alerting by doing the following:
Go to the navigation bar and select configure->correlation searches.
Find the Multi-KPI-Alert that you just created
Press Edit->By correlation search editor
Expand the "Advanced Options" panel.
Check "Send email"
Fill out the required fields for the email action.
Save
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