This bit of experience has been “grabbed-as-is” from another blog. See page bottom for details…
If you’ve tried using the Postie plug-in (version 1.1.1, anyway) with WordPress 2.3, you’ve probably seen that the feature related to Categories do not work. The database schema changed for WordPress2.3, and Postie was reading categories directly from the tables with SQL calls.
Thanks to efforts of a few others, who nearly got it right, I managed to cobble together a fix that allows emailed posts to be categorized and add a default category to emailed posts that do not include category details. Credit/kudos to Olivier and Greg and Benjamin for comments and work referenced on the Postie page.
I don’t mean to detract from the work these gentlemen did before I stumbled across the same problem. I tried implementing their corrections, but had a different problem that nobody else mentioned: only a fraction of my established categories appeared in the list on the config page. It had similar problems locating Categories specified in the email subject. The solution was to provide an additional parameter in the call to get_categories(). For efficiency, I also pulled the call to create a local list of categories out of a foreach loop, so that the same work wasn’t being done multiple times, in the case of an email specifying multiple categories. (Always optimyze…)