The poster at Apathy Online has developed a quick hack for Panther Mail users that will give them the “Outlook-like” three-pane layout.

Tiger Mail users can use Aaron Harnly’s excellent Letterbox plugin . However, despite a few positive reports, Aaron doesn’t promise seamless operation in Panther Mail.

If Letterbox fails you in Panther, this could be the fall-back you are looking for.

The end result looks like this:

Image from ApathyOnline

Installing it is easier than you might think.

First, quit Mail. Then navigate to it in your Applications folder and right-click on Mail’s icon. Select the “Show Package Contents” option:

Then navigate through the Contents and Resources folders to the English.lproj folder. (Or the lproj folder for the language you use.)

Open it. Find the MessageViewer.nib file:

Back-up the original file before you do anything, either making a duplicate in the same place or copying it to the Desktop.

Then right-click on the MessageViewer.nib icon, choose the “Show Package Contents” option again and replace the files inside with the three modified files from ApathyOnline.

Restart Mail.app and enjoy.

Disclaimer: I have not tested this myself, no longer having a Mac with Panther installed. Also, since I can’t remember that far back, I have simply assumed the layout of the Mail package is the same. If it isn’t, I hope that someone will tell me.