After the upgrade, some sites might be unable to access SquirrelMail. To resolve this, you need to upgrade the SquirrelMail file config.php.
To upgrade the SquirrelMail file config.php:
root user. /home/virtual/<domain>/var/www/squirrelmail/config/config.php using the following command:cp /home/virtual/<domain>/var/www/squirrelmail/config/config.php <directory>/config.php.bak where <directory> is the directory to which you want to copy the file.
/etc/virtualhosting/templates/sqmail/var/www/squirrelmail/config/config.php to the broken site's directory (/home/virtual/<domain>/var/www/squirrelmail/config/config.php).config.php file has been modified by Site Administrators, then they should merge the old and the new config.php files.