Group by subject
If you frequently correspond with a certain person/people, turn on the To expand or collapse a list of messages in a thread, click the subject of the message. To view any email in a thread, click on the line containing that email.option (to the right above the message list). Your emails will be grouped into message threads.
What you can do with email threads
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.
Note. Note that the messages stored in the Spam, Trash and Drafts folders are never grouped.
You can also move within a message thread by using the message page.
To ungroup messages, disable theoption (to the right above the message list).
What you can do with emails inside threads
Restriction. Messages can be managed within a thread if you enable the open message in list of messages option.
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.