Change the Columns Shown in Mail for Windows
To set the columns shown in the Mail for Windows mailbox view, open Mail for Windows and:
Open Mail for Windows. Hover mouse between the Email pane and Preview pane until you see a double-arrow (resize). Click and drag to the right (to increase) or to the left (to decrease) for column resizing.
You can only resize the columns to a certain point. There will always be 3 panes including the Folders pane, Email pane, and the Preview pane.
