When using the Outlook Web App, your emails may be showing as individual messages. This means any replies or forwards will not be included when viewing an email.
The below video and proceeding guide will go through changing the Outlook Web App to show emails by conversations.
In the screenshot below, I replied to this email. But I would have to check my Sent Folder for the reply.
Instructions:
1. At the top-right corner, select the Settings Icon (gear).
2. Then go to the bottom of the Settings panel and select View All Outlook settings.
3. The Settings window will pop up. Select Mail.
4. Select Layout.
5. Under Message Organization, select Show email grouped by conversation.
6. Select Save.
7. Close the Settings window.
Your emails will now show replies and forwards. You can click on any collapsed messages to view them entirely.
Note: The default is to show the newest message on top. If you want to change this, go back to All Outlook Settings > Mail > Layout > Message Organization. There will be new settings to adjust there.