How to prevent Outlook 2010 from downloading a message body automatically when I select it?

I configured Outlook 2010 to send/receive my mail through IMAP account. When I click on the Inbox folder in the Navigation pane to the left I get all my new messages in the view pane to the right (headers only). When I select a message Outlook automatically starts downloading the message body and the message body appears in the reading pane bellow. How to prevent this? I want to do that manually by right clicking the message and select [download message] or something. Reason why I want this is that I sometimes I get huge size emails I am not intrested in reading them. I just want to delete them without having to download them. Thanks