Further testing lead me to have to change the settings to the IMAP standard, despite the fact that I'm not using IMAP. Thus, my settings are now:
// NOTE: Use folder names with namespace prefix (INBOX. on Courier-IMAP)
$rcmail_config['drafts_mbox'] = 'INBOX.Drafts';
// store spam messages in this mailbox
// NOTE: Use folder names with namespace prefix (INBOX. on Courier-IMAP)
$rcmail_config['junk_mbox'] = 'INBOX.Junk';
// store sent message is this mailbox
// leave blank if sent messages should not be stored
// NOTE: Use folder names with namespace prefix (INBOX. on Courier-IMAP)
$rcmail_config['sent_mbox'] = 'INBOX.Sent';
// move messages to this folder when deleting them
// leave blank if they should be deleted directly
// NOTE: Use folder names with namespace prefix (INBOX. on Courier-IMAP)
$rcmail_config['trash_mbox'] = 'INBOX.Trash';
// display these folders separately in the mailbox list.
// these folders will also be displayed with localized names
// NOTE: Use folder names with namespace prefix (INBOX. on Courier-IMAP)
$rcmail_config['default_imap_folders'] = array('INBOX', 'INBOX.Drafts', 'INBOX.Sent', 'INBOX.Junk', 'INBOX.Trash');
This appears to work correctly.
I'd still like to know how to get the check-box settings applied to all users, without having them go in manually and changing them. Anyone?