From iRedMail

THIS UPGRADE TUTORIAL IS A DRAFT, DO NOT APPLY IT.

General

Enable case insensitive user authentication in Roundcube webmail

Please change below setting to true in Roundcube webmail config file 'config/main.inc.php' to enable case insensitive user authentication. The config file should be:

• /var/www/roundcubemail/config/main.inc.php on RHEL/CentOS/Scientific Linux
• /usr/share/apache2/roundcubemail/config.inc.php on Debian/Ubuntu
• /srv/www/roundcubemail/config/main.inc.php on openSUSE
• /usr/local/www/roundcubemail/config/main.inc.php on FreeBSD

$rcmail_config['login_lc'] = false;