In your Mac's menu bar, click the View menu and choose Show as Conversations.
Microsoft Outlook for Mac is an email application used to send and receive email messages. In Outlook, you can view email messages by conversation so that messages in a folder with the same subject are grouped together in the message list. The most recent new message is placed at the top within each conversation. You can also turn off viewing email messages by conversation. Instructions can be found below.
1) Open Microsoft Outlook if it is not already open.
2) In the bottom left-hand corner, click the "Mail" icon.
3) In your Mac's menu bar, click the View menu and choose Show as Conversations. This option is a toggle; putting a checkmark next to it will enable the feature, and removing the checkmark will disable the feature.
Your preference for conversation view has been set.