We all have our preferences when it comes to how we work. Our Microsoft Outlook settings are no different.
Many people like to have their inbox set up with the reading pane to preview emails at a glance without fully opening them. This is a common practice that, unfortunately, opens up users for unwanted viruses and threats via email.
Emails sent to your inbox containing viruses or malware will install the threats when the emails are viewed in the preview pane, whether or not you've fully opened them or not.
To avoid this potential danger, simply turn off your Outlook reading pane. To do this, go to View > Reading Pane > Off.
This should be done for Outlook Web Access as well because the threat is the same.