One of the new features of Outlook 2013 is Conversation view. When Conversation view is enabled, messages are organized by conversation, that is to say, messages with the same Subject line appear as Conversations.
You can then easily work with these Conversations.
To turn Conversation view on:
With Conversation view turned on, Conversations will show up in your message list as indicated by an icon showing that there are multiple items.
Click the icon to view all messages in the Conversation.
When you click the Conversation header, that conversation appears in the Reading pane. The newest message in the thread appears at the top.
If there is a Conversation that you would like to not appear in your inbox, you can remove it. To remove a Conversation:
If you would like to remove some messages from a Conversation, you can clean up that Conversation.
To clean up a Conversation: