Yesterday I released the Posterous Importer plugin. Like the Vox Importer plugin, this one depends on the WP_Importer base class, so make sure to install that first. This plugin is based on the WordPress.com core importer. You can read about that on the WordPress.com blog.
I know it’s not ideal to make plugins that depend on other plugins, but right now the core import API does not have the functionality that I need. I’m working on that part though. Getting patches into core is not easy.
When you have the Posterous Importer installed, click on Tools -> Import from the WordPress admin screen. You should see Posterous in the list of importers.
Type in your Posterous host name, user name, and password. Click the Submit button. The importer will now validate your login credentials with Posterous.
If the authentication succeeds, the import will now begin. Depending on the amount of posts, comments, and attachments the import may take a while. You can not navigate away from this page while the importer is working.
If the importer times out or runs out of memory during the import, just keep restarting it until it finishes. The importer keeps track of what it has already imported so that you don’t end up with duplicate posts.