The menu on the top left provides ample options to change the view. One of them is "grouping".
They roughly following the logic of PTPT: you can group along one of the dimensions:
Some groupings will not make sense, however for sake of consistency, we kept the general logic. But you can, for example, group your emails by Time, in this way, you'll get your emails grouped by day or week, etc.
Note the arrows next to the group menus. If you tap on them, you can change the different versions of that grouping. For example when grouping by Time, you can toggle different time resolutions like "day", "week" etc.
When toggling through the different variations, you'll notice at "Things" that there'll be "cluster by similarity". This will collect all emails to one topic into one group. For example, you'll get all emails from a project into one group (doesn't have to be a discussion thread), one group of flight confirmations, one for invoices etc. Since this is a computation heavy calculation, it may take a couple of seconds...