I have been using Postbox for quite some time now since I no longer only use gmail accounts (had this been the case I would have been using Mailplane). A new answer in the postbox forums regarding two line message items showed an image of Mail.app with the WideMail plugin which I had previously used back in my Mail.app days. However, WideMail has since my last use implemented a new column for Mail.app which lets you customize a two-line message item display, so I moved back to Mail.app to try it out.
I also downloaded a fresh version of Mail Act-On, a plugin for Mail.app which I also used before. It to as received a few updates. To my delight, Mail Act-On now lets you have several rules bound to the same key, and are applied to the messages which fit each rule. In my case, I have four accounts in Mail.app. In Postbox, each mail account would have a configured “Archive” folder which e-mail that is selected for archival is moved to. Mail.app does not have this built in, but now with the new version of Mail Act-On I have one Archive rule for each account, all bound to the ‘Ctrl+A’. Now when I press Ctrl+A, the email is moved to a folder depending on which account the email is located in!