How to Sort Messages by Conversation in Microsoft Outlook

Organize your Outlook messages by sorting them by conversation.

This feature works the same in all modern versions of Microsoft Outlook: 2010, 2013, and 2016.

Select the View tab of the Ribbon, and in the Messages group, check the Show as Conversations check box.
In the dialog box, select an option to display conversations in all folders or the selected folder only.
Messages are now sorted by conversation.