In Postbox, there are two ways to display your messages: Classic and Vertical View. Each offers a useful yet different approach to reading your messages. To switch between Classic and Vertical View, go to View > Layout and select the desired layout. Try them both to see which one is right for you.
Here are the main differences:
Classic View
In Classic View, your messages are displayed in a list with each message's attributes available in columns. This view resembles a spreadsheet, where columns can be sorted, rearranged, revealed and hidden, so you can quickly find the messages you're looking for. Clicking on each column header will sort your messages by that column, and clicking a second time will switch the sorting from ascending to descending, or vice versa. You can simply drag columns to rearrange them and to add or remove columns from view, just right-click (control + click on Mac) any column header to reveal a menu which lists all the options.
When selecting a message in Classic View, a preview will appear in the Message Pane, found in the lower half of the Postbox window. You can hide and show the Message Pane by going to View > Show > Message Pane.
Vertical View
In Vertical View, your messages are listed on the left side of the Postbox window, next to the Accounts and Folders Pane. Each message item takes up two rows to display important information. A message's sender, subject, date, and status are all represented, in addition to a thread count indicator which discloses a list of messages that are related. Although there is just one column, clicking on the header will sort your messages in chronological or reverse-chronological order, and going to View > Sort By will offer many more sorting options.