Courier uses a different folder structure than the IMAP server included with SME. To get it to work properly, you'll need to change the IMP configuration. Here's what you'll need to do:
# mkdir /etc/e-smith/templates-custom/home/httpd/html/horde/imp/config/servers.php
# cd /etc/e-smith/templates-custom/home/httpd/html/horde/imp/config/servers.php
# cp /etc/e-smith/templates/home/httpd/html/horde/imp/config/servers.php/40Servers .
# pico 40Servers
You'll need to change two lines in here:
'folders' => '', // this is two single quotes, not a double quote
'namespace' => 'INBOX.', // be sure to include the trailing period
Save the file, and
# /sbin/e-smith/expand-template /home/httpd/html/horde/imp/config/servers.php
You should be ready to go.