It's nice to have things your way, at least most of the time. That includes modifying Mail to display your information just the way you want it. By default, the columns will show you certain information such as who sent you an e-mail, the date, the subject, etc. But maybe I want to see the size of an attachment, or have the mailbox that a message is in displayed in the main window. No sweat.

To add columns not currently in your view, simply right-click (Ctrl+click) anywhere in the header bar, then choose to turn on the item you want. Conversely, uncheck an item to turn it off.

Once you have the columns turned on and off that you want or don't want, it's easy to move them to a different order. Simply drag and drop the column to where you want it. It is a Mac afterall!

Check out this sample below: