Looks up IP addresses and domain names in so-called "DNSRBLs". I say "so-called" because there's no real reason why they should be block lists.
This project takes significant inspiration (but no code) from https://github.com/logic/rblcheck. The biggest benefit over the original is IPv6 support, which is unfortunately lacking from most RBL tooling. We also support allow-lists, and if an IP or name is found in one of the allow-lists then we report not blocked.
```
$ dabl --help
dabl 0.4.0
USAGE:
dabl [FLAGS] [OPTIONS]
FLAGS: -h, --help Prints help information -q, --quiet Only output errors -V, --version Prints version information -v, --verbose Output debugging information
OPTIONS:
-a, --allow
ARGS:
The Author uses dabl to restrict access to his IMAP service using TCP Wrappers.
Regular DNSBLs aren't intended to restrict access to consumer-facing services; you probably don't want to block the "Dial-Up Address List", for example.
Spamhaus has a subscription list called "AuthBL" which contains IPs observed attempting credential stuffing.
I have no interest apart from being a very happy user of their free subscription.
Adding this line to /etc/hosts.allow and enabling the relevant configuration in your service will let you query the lists of your choice.
imap, imaps: ALL: aclexec /usr/local/bin/dabl -a al.aylett.co.uk -b bl.aylett.co.uk -b YOUR_KEY_HERE.authbl.dq.spamhaus.net %a
Note that the Author's allow and block lists are not general-purpose, and you'll need a key for SpamHaus. Copy and paste at your own risk! If you want to run your own DNS allow- and block-lists, you may find rbldnsd to be useful.