Emails being viewed by conversations rather than single email/thread

https://support.office.com/en-us/article/view-email-messages-by-conversation-0eeec76c-f59b-4834-98e6-05cfdfa9fb07

View email messages by conversation

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By default, when you add most account types to Outlook 2013, 2016, or Outlook for Office 365, your messages are displayed in Conversations. A conversation includes all messages in the same thread with the same subject line. Older versions of Outlook may not show conversation view enabled by default.

Newer versions Office 2007

From any email folder, such as your inbox, clickView>Show as Conversationsto toggle Conversation view on or off.
ClickAll mailboxesorThis folder.

Conversation that include multiple messages are identified in the message list by Collapsed Conversations icon . Clickto expand the Conversation.

Example of split Conversations in Conversations arrangement view

Within each Conversation, messages are sorted with the newest message on top. You cannot change this sort order.

Example of a Conversation with splits fully expanded in the message list

When you receive a new message that’s part of a Conversation, the whole Conversation moves to the top of your message list.

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.

Change Conversation options

There are several conversation options you can change.

From any email folder, such as your inbox, clickView>Conversation Settings
Select any of the available options.
- Show Messages from Other FoldersUse this option to display messages in the conversation that have been moved to other folders as well as messages you've sent that are stored in your Sent Items folder.
- Show Senders Above the SubjectSelecting this option shows the sender names at the top of the conversation rather than the conversation subject.
- Always Expand Selected ConversationThis option applies only to the currently selected conversation. The conversation selected when you check this box will always appear expanded.
- Use Classic Indented ViewClassic indented view shows messages in the conversation indented based on their position within the conversation.