When a message is selected, the left side of the screen displays a Conversation History, which includes the message sent to Inbox along with the five most recent messages sent to or from the associated record in the past 60 days.
The specific Inbox message you are viewing uses an orange background to distinguish the message from the others in the Conversation History. Additionally, this specific message is expanded by default, and all other messages in the Conversation History are collapsed. Click on the message header to toggle the message visibility.
Displaying other recent messages in the Conversation History relies on the message being assigned to a person record. If the message is not yet assigned to a person record, or if there is a different record that the message should be assigned to, follow the instructions above to update the Person Record Assignment.