The reading pane in Microsoft Outlook is a took that allows the user to quickly view the contents of an email message. The down side to this is that it causes an open message process that can cause some e-mail borne viruses to activate as soon as they enter the Inbox. For security purposes we recommend that end users review the subject and who the message is from before opening the message to ensure they are not allowing something malicious to run on their computer. Closing the reading pane helps to ensure that the end user takes the time to check the message details first before opening it.
How to Turn Off Reading Pane