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.