These buttons switch the view of your Inbox from ‘List’ view, which shows all emails, to ‘Threads,’ which group original emails together with their responses.
Shows the email in List View
Shows the emails in groups or by thread
The ‘Select’ drop-down menu offers the options to select ‘All,’ ‘Current page,’ ‘Unread,’ ‘Flagged,’ ‘Invert,’ and ‘None.’
In the ‘Threads’ mode, the ‘Threads’ drop-down options become available, allowing you to control how your grouped emails are displayed.