View message list by Conversations
When you switch to Conversations arrangement view, messages that share the same subject appear as a group or collection of messages.
Click View > Show as Conversations.
Click All folders or This folder.
Conversations are identified in the message list by . Click to expand the Conversation.
Within each Conversation, messages are sorted with the newest message on top.
When you receive a new message that’s part of a Conversation, the whole Conversation moves to the top of your message list. When you click a Conversation header in the message list, the Conversation shows in the Reading Pane, with the newest message on top.
Any Conversation that includes unread messages has a bold subject and the count of the unread messages appears next to the subject. When you click to expand the Conversation, any unread message has a bold heading.
When there are two or more responses, the Conversation can split into multiple related, but separate, Conversations. The latest message in each split appears when you click a Conversation. Click one of the split Conversations to show the messages from that split in the Reading Pane, with the latest message on top.
To change how Conversations arrangement works, such as whether to include messages that are saved in other Outlook folders, see Change options for viewing messages in Conversations.