To disable the sending of listchanges information from APT run the following command:

dpkg-reconfigure apt-listchanges

Then select None as Method to be used to display changes. Confirm all other requests with the default selected value.

If enabled the debsecan-package will send a daily email with all vulnerabilities in installed packages on the system. To disable remove the MAILTO and the cron entry from the file /etc/cron.d/debsecan by commenting them out.