Multiple DB connections: http://dbcharmer.net/
Mail Servers: http://kolab.org/overview http://www.iredmail.org/ http://myroundcube.com/myroundcube-plugins/register-plugin/iredmail-guide http://www.howtoforge.com/iredmail-mail-server-with-ldap-postfix-roundcube-squirrelmail-dovecot-clamav-spamassassin-amavisd-debian-5.0.1 https://bitnami.com/stack/roundcube/virtual-machine http://web.appstorm.net/how-to/setup-your-own-webmail-with-roundcube/ http://www.horde.org/ https://bitnami.com/stack/roundcube