Conversation View in Outlook on the Web
Conversation view clusters your messages together, based on Subject.
This article applies to: Outlook on the Web
Microsoft frequently updates the design of Outlook on the Web, so your version may not match exactly the description given here.
By default, Outlook on the Web displays your messages with Conversion View turned on, which clusters your messages based on Subject, as shown in the example below:
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.
If you delete a message while in Conversation view, you actually delete all messages in that thread.
To turn Conversation View on or off, select the folder where you want to change the setting, then, in the heading row at the top of the list of messages in that folder, click the downward-facing arrow. From the menu that appears, in the View as section, select either Messages or Conversations.