Super!
I have used this script now via cron and everything seems to work fine, including a significant reduction of "denied" mail attempts in the mail log.
I've added the following lines to keep the last 20 url lists, compressed with 7z (which I prefer for compression), for analysis (if needed):
7z a -mx9 "${current_datetime}.7z" "formatted_$output_file"
rm "formatted_$output_file"
rm "$output_file"
ls -td *.7z | grep -v '/$' | tail -n +20 | while IFS= read -r f; do rm -f "$f"; do>
Also: If you use the script, don't just blindly add url-lists. I already managed to lock myself out once by adding the "standard" Firehol list (https://iplists.firehol.org/files/firehol_level1.netset)