Courier mail services

Install rpms like "courier-imap", NOT "courier-imapd" unless you want to
run Courier's mail server instead of Exim/Sendmail.

Maildir:
Courier uses Maildir format, which is pretty much the opposite of UNIX
mail folders.  1 file per message.
I thing subfolders are always nested, with the Inbox at the root, with
convention of $HOME/Maildir.  Here's the Exim config:

    local_delivery:
        driver = appendfile
        directory = ${home}/Maildir
        maildir_format = true

The directory is created automatically, as needed.
Looks like by default everything is created as $user.$user with umask 077.

GENERAL
None of the Courier products (at least the non-d products) have
/etc/sysconfig/* config files.
Set *START values of all /etc/courier/SERVICENAME files.

AUTHENT
You MUST run authdaemond via /etc/init.d/courier-authdaemon to run any
service.
Configured via /etc/authlib/*rc (n.b. *rc are not init scripts, but config
files).
Most importantly, set authmodulelist.

imapd:  (The *s and pop services probably work exactly the same).
Primary config file:  /etc/courier/SERVICETYPE
You just run the the "couriertcpd" via /etc/init.d/courier-imap.
This init script will invoke the authdaemond init script if necessary).
Configged via /etc/courier/SERVICETYPE (/etc/courier/*.cnf is just
for cert details).
/etc/courier/SERVICETYPE is parsed and also sourced by init script.
IMPORTANT:  Do not set DEFDOMAIN in configfile.  This sets the user names.