I love Postbox, but at Palantir.net, we do not have the option to purchase an email client for our workstations. As my Postbox beta expired, I needed to export from Postbox into the OS X Mail.app. This migration is very simple.
The key fact to know is that Postbox stores its mail in the same format that Thunderbird uses. Mail.app already supports importing from Thunderbird. Assuming you already have an account set up in Mail.app, go to the
File menu and choose
"Import mail" dialog
The import dialog suggests a path to Thunderbird. However, the path that should be used for Postbox is
~/Library/Ppostbox/Profiles (where the
~ is shorthand for your home directory).
Once you click
Continue, Mail.app will import all of the folders and messages, including the Archive and Sent mailboxes. As far as I can tell, tags/labels are not imported.
When the import is finished, you should have a new
Import folder in Mail.app's
On My Mac section.
All of your old folders should be imported into the new
Local Folders folder. You may notice that certain POP3 folders were imported with the name of my POP server. And all of the messages are marked as unread.
From there, you should be able to re-organize as you see fit.