How does resizing of columns work?

In all viewers with columns, the subject column is automatically resized to fill up any remaining space. To resize a column, drag the right border of the header of the column you want to resize. If you make the subject column wider all other columns will be made smaller. If you make the subject column smaller all other columns will be made wider. If you make another column wider, the subject column will be made smaller and vice versa.

The automatic resizing of the subject column can be turned off by right-clicking a column header and unchecking the "Automatic column resizing" menu item.