The first one is to avoid having a scheduled task running at least every minute to keep the list updated.
How were you planning to get the lists into postfix, and keep them updated?
The second one is that I only want to add the relevant firewall rules to the mailserver. I don't know how many rules you can have before it starts to effect performance.
With ipsets (or nftables setc, etc) it's one rule ... e.g., https://www.thegeekdiary.com/how-to-use-ipset-command-in-linux/
