Courier-imap 4.x no longer supports external authentication. With courier-imap 3.x we used auth_imap from qmail-ldap.

We can use binc imap instead and it will work with auth_pop.

aptitude install bincimap

rsync -axvPS --delete /usr/share/doc/bincimap/etc/bincimap.daemontools/ /var/qmail/supervise/bincimap/
rsync -axvPS --delete /usr/share/doc/bincimap/etc/bincimaps.daemontools/ /var/qmail/supervise/bincimaps/

find /var/qmail/supervise/ -name run | xargs chmod 755

echo Maildir > /var/qmail/control/defaultdelivery

<strong>/var/qmail/supervise/bincimap/run</strong>:

export POP3_LOGLEVEL=2

exec    tcpserver -c 100 -u vmail -g vmail      \
    -l $(hostname) -HDRP                        \
    0 143                                       \
    /usr/sbin/bincimap-up                       \
    --logtype=multilog                          \
    --conf=/etc/bincimap/bincimap.conf --       \
    /var/qmail/bin/auth_pop                     \
    /usr/sbin/bincimapd `cat /var/qmail/control/defaultdelivery`

<strong>/etc/bincimap/bincimap.conf</strong>:

Authentication {
    allow plain auth in non ssl = "yes",

cd /service

ln -s /var/qmail/supervise/bincimap .
ln -s /var/qmail/supervise/bincimaps .