SaneSecurity offers unofficial phishing and scam signatures for ClamAV. The usage page lists a variety of download scripts. I opted for the "download script 1". This script requires the ClamAV command line interface and Curl for operation. The clamav and curl packages fulfil these requirements on Debian.

/usr/local/sbin# wget -O update_sanesecurity [[][]]

/usr/local/sbin# chmod +x update_sanesecurity

I would also recommend to change the stderr_loglevel from none to error, so cron will notifiy you about errors by email.

# Log messages with this or greater severity to standard error