By default, email messages in your Microsoft Outlook Inbox are grouped and arranged by date.
Messages in your Microsoft Outlook 2010 Inbox and other mail folders can also be organized by date and arranged by Conversation. When Conversations is turned on, messages that share the same subject appear as Conversations that can be viewed expanded or collapsed. You can quickly review and act on messages or complete Conversations.
For more information about Conversations, see View email messages by Conversation.
Turn on or off Conversations
On the View tab, in the Conversations group, select or clear the Show as Conversations check box.
Click All folders or This folder.
Change Conversations settings
You can change the behavior of Conversations, such as whether Conversation include messages that are saved in other Outlook folders.
On the View tab, in the Conversations group, click Conversation Settings.
Note: The Show as Conversations check box must be selected to enable the Conversation Settings command.
Click the option that you want.