Fix Plesk Roundcube Webmail 500 Error: Database & PHP Configuration Solutions

tail -n 50 /var/log/roundcube/errors.log

Or, on some Plesk installations:

tail -n 50 /usr/share/roundcube/logs/errors

The log almost always names the exact problem: a database connection error, a missing PHP extension, a timezone warning that escalated to a fatal, or a session write failure.

tail -n 50 /var/log/plesk/nginx/webmail.error.log

Or for Apache:

tail -n 50 /var/log/plesk/apache/webmail.error.log

PHP fatal errors are typically captured here when Roundcube's own log isn't writable.

grep -i "roundcube\|webmail\|fatal\|error" /var/log/php-errors.log | tail -20

plesk bin php_handler --list | grep webmail

Note the PHP version (e.g., 8.1, 8.2).

php -r "phpinfo();" | grep -i "pdo_mysql\|mysqli"

If the extension is missing, install it via Plesk's PHP settings:

plesk bin php_handler --set-webmail-handler --version=8.1

On CentOS/AlmaLinux/CloudLinux:

yum install php81-php-mysqlnd php81-php-pdo

On Debian/Ubuntu:

apt install php8.1-mysql

After installing, restart PHP-FPM:

systemctl restart plesk-php81-fpm

php --ini | grep "Loaded Configuration"

Or check the Plesk-managed php.ini path, typically at:

/opt/plesk/php/8.1/etc/php.ini

[Date]
date.timezone = "UTC"

Or replace UTC with the server's actual timezone (e.g., America/New_York, Asia/Kolkata). Verify the timezone string is valid:

php -r "echo date_default_timezone_get();"

systemctl restart plesk-php81-fpm

cat /etc/roundcubemail/config.inc.php | grep db_dsnw

Or on some Plesk versions:

cat /usr/share/roundcube/config/config.inc.php | grep db_dsnw

This shows the database user and password Roundcube uses. Note the username.

mysql -u root -p -e "SELECT user, host FROM mysql.user WHERE user LIKE '%roundcube%';"

Then check grants:

SHOW GRANTS FOR 'roundcube'@'localhost';

mysql -u root -p -e "ALTER USER 'roundcube'@'localhost' IDENTIFIED BY 'new_strong_password';"

Then update the password in config.inc.php to match.

Navigate to https://webmail.yourdomain.com/installer/ in a browser (you may need to temporarily enable the installer in config.inc.php by setting $config['enable_installer'] = true;). Run the database initialisation step to recreate missing tables.

ls -la /var/lib/php/sessions/
ls -la /tmp/roundcube-temp/

If these directories are owned by root and not writable by the webmail PHP user, sessions fail silently and return 500.

chown -R apache:apache /var/lib/php/sessions/   # CentOS/AlmaLinux
chown -R www-data:www-data /var/lib/php/sessions/ # Debian/Ubuntu
chmod 1733 /var/lib/php/sessions/

rm -rf /usr/share/roundcube/temp/*
rm -rf /usr/share/roundcube/cache/*

plesk repair mail -all

This re-checks webmail dependencies, resets file permissions, and verifies the database schema.

plesk installer --select-product-id plesk --select-release-current --upgrade-installed-components

This upgrades all Plesk components including Roundcube to the version tested with your Plesk release.

plesk installer --select-product-id plesk --select-release-current --install-component roundcube