Update 20100331:
Important note: You shouldn’t adjust this preference by editing prefs.js directly as with current versions of Thunderbird, you either risk losing all your settings or that the setting doesn’t have any effect at all. Instead, you should do the following (as described in Thunderbird Help & Tips):
- Open Thunderbird’s Config Editor
- search for the preference mail.check_all_imap_folders_for_new, and change its value to true.
Alternatively, you might want to take a look at the additional hints (e.g. how to configure Courier IMAP accordingly) in Mozillazine’s knowledge base about how to check for new mail in other folders.
add
user_pref(“mail.check_all_imap_folders_for_new”, true);
to your profile’s prefs.js file.
it’s strange this isn’t the default setting. and there isn’t a gui for it either. perhaps an indication for a bad implementation causing unnecessary overhead? [source: Hidden Mozilla Prefs]