This article applies to: Outlook 2016 for Mac
The following link will take you to a Microsoft help page:
But before you go, here's some additional information you may find helpful.
By default, Outlook 2016 for Mac displays your messages in order of Date Received. You can change the sort order by clicking the heading in any column, or by selecting an option under the View menu, Arrange By.
Another way to arrange your messages is Conversion View, which clusters your messages based on Subject. The original message, your replies, and other people's replies are all displayed together.
Conversation view can help by giving you a compact record of an entire thread, but it can be confusing if you have more than one conversation with identical Subjects, or if you prefer to see your messages in strict chronological order.