Turn on grouping by subject to link messages into threads. To view any email in a thread, click on the line containing that email.
What you can do with email threads
To expand or collapse a list of messages in a thread, click the subject of the message.
The message thread displays all emails grouped by a selected subject, even if they have different recipients or senders, or are in different folders. Messages are only grouped by subject. Senders and recipients do not factor into grouping.
What you can do with emails inside threads
You can manage all emails in a thread together (for example, mark all as read, delete or forward them all). To do this, click the button in the subject line.
Use the buttons to move between email threads.