sudo apt-get install -y wget lsb-release gnupg
wget -q -O - http://powerman.github.io/courier-imap/public.key | gpg --dearmor | sudo tee /etc/apt/keyrings/courier-imap.gpg >/dev/null
echo "deb [signed-by=/etc/apt/keyrings/courier-imap.gpg] https://powerman.github.io/courier-imap/apt/$(lsb_release -cs) $(lsb_release -cs) main" | sudo tee /etc/apt/sources.list.d/courier-imap.list
apt-get update

apt-get install libcourier-auth \
    libcourier-auth-ldap        \
    libcourier-auth-mysql       \
    libcourier-auth-pgsql       \
    libcourier-auth-pipe        \
    libcourier-auth-sqlite      \
    libcourier-auth-userdb

apt-get install courier-imap

apt-get install -y gnutls-bin
/usr/lib/courier-imap/share/mkdhparams
/usr/lib/courier-imap/share/mkimapdcert
/usr/lib/courier-imap/share/mkpop3dcert