in VestaCP

Fix Roundcube after upgrading to PHP7.2

apt install roundcube-core roundcube-mysql roundcube-plugins
wget http://c.vestacp.com/0.9.8/debian/apache2-webmail.conf  -O /etc/roundcube/apache.conf
nano /etc/roundcube/debian-db.php (enter password)
cd /usr/share
mv roundcube roundcube-bk
rm -r roundcube
wget https://github.com/roundcube/roundcubemail/releases/download/1.3.7/roundcubemail-1.3.7-complete.tar.gz
tar -xvf roundcubemail-1.3.7-complete.tar.gz
mv roundcubemail-1.3.7-complete roundcube
rm -r /usr/share/roundcube/installer
service apache2 restart
service nginx restart

To fix Rouncube SMTP 550 error:
nano /etc/roundcube/config.inc.php

update values:
$config['smtp_server'] = '%h';
$config['smtp_user'] = '%u';
$config['smtp_pass'] = '%p';