Another keyboard combination in Outlook that is often overlooked is ALT + DEL on an email message. This brings up the Clean Up Conversation dialog box (and also allows you to adjust the Clean Up settings – this can also be found under the Outlook Options under Mail.). The Clean Up button is also available on the ribbon.
The idea behind conversation cleanup is to automatically remove redundant messages in a conversation. The basic idea is that if that contents of a message are completely contained in a reply, the previous message is moved to the Deleted Items.
This feature is available in Outlook 2010 and Outlook 2013.