jkOnTheRun posted about Letterbox which I ran for a while. The only thing that bothered me was that the default columns Mail.app shows in the message list required that, in order to see everything, the center pane be a little wider than I typically like. Then I noticed that a commenter on that post recommeded WideMail which has the added benefit of breaking down the message metadata into two lines in one single column of the message list (similar to Outlook). WideMail also seems to have a bit more flexibility in its configuration options.

For now, I am running WideMail and am really liking it. I haven’t had any issues so far. The only concern I have is that the developer’s blog has not been updated since March of 2008 so I wonder if development has stopped. Letterbox also seemed stable for the brief period in which I ran it so I think it is a good option as well.