[Dovecot] Odd Feature Request - RBL blacklist lookup to prevent authentication

I would like to have a list of IPs (hacker list) that I can do a lookup on so that if anyone tries to authenticate to dovecot they always fail if they are on my list.

I have the list - and the list is available as a DNS blacklist.

I'd like to have it work with both local IP lists or RBL lookup.

The idea is so hackers from known IP addresses never succeed.

If Dovecot provides the feature I have about 1/2 million IP addresses of known current hackers to block.

Anyone else interested in this?