An e-mail with subject "RBL Check on *: [0] failures" can be sent from a Linux server which runs CSF (ConfigServer Firewall).

The e-mail can contain example this:

Checked * (PUBLIC) on Sun Aug 20 00:00:03 2017

Checked * (PUBLIC) on Sun Aug 20 00:00:17 2017
The e-mail source code shows this in my case:
X-Source: /usr/local/cpanel/3rdparty/perl/524/bin/perl
X-Source-Args: /usr/local/cpanel/3rdparty/bin/perl /usr/sbin/csf --rbl [email protected]

So it is CSF that sends the e-mails. Here is the file that can be modified: /etc/csf/csf.rblconf
So there i can maybe disable as it TIMEOUTs.

in that file i can also add new RBLs by adding lines like:
To disable all RBL reporting e-mails, i go to WHM, Plugins, ConfigServer Security & Firewall, Check for IPs in RBLs (button), and set "Generate and email this report "Never" to the email address [email protected]