A new feature in Outlook 2010 is the Conversation Clean Up tool. It will delete messages from a “conversation” while preserving all of the information. Outlook is smart – it can check whether a later message contains the text of an earlier message – and then it deletes the earlier messages (which have the repetitive text).
For example, you may be emailing back and forth with a colleague, replying to a message that was sent. Outlook can “see” that the series of messages contain the same text, so it will delete the older versions.
To apply this to your Inbox, first go to the View tab and click the box next to Show as Conversations.
To clean up the conversation, right-click on the message and choose the Clean up Conversation option. It’s a great way to clear out some of that email clutter.