Here is how to add a custom message to every outgoing email in Roundcube:
Edit the config/default.php file:
nano /usr/local/cpanel/base/3rdparty/roundcube/config/config.inc.phpand add the following to it:
$config['generic_message_footer'] = 'message.txt';
$config['generic_message_footer_html'] = 'message.txt';Now in root folder of roundcube, create a file named message.txt with the desired content:
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This email was sent from Roundcube cPanel.