Feature is implemented and tests were created in TTS-NG. I've tested it locally (on a single node deployment) and using test cases and all was working fine.

PR https://github.com/tigase/tigase-server/pull/209

Looks OK. Minor comments.

Please include documentation (what it is, what's the purpose, how it operates / how to configure it);

EDIT: shouldn't we add xmppbl.org by default to repository (possibly as configurable option like useDefaultServers)? I think it would make usage of the feature easier.

shouldn't we add xmppbl.org by default to repository (possibly as configurable option like useDefaultServers)? I think it would make usage of the feature easier.

I'm against adding any block list automatically, especially those that are out of our control. Moreover, I doesn't feel OK to add sending any requests to other services just because someone could decide it is useful. Some people (even not understanding what it does and how) could consider this harmful and privacy invasive.

Moreover, even other developers, ie. Prosody developers behind this feature/service, decided not to include their own service as a hardcoded blocklist.

OK, understood.

Still, any sort of documentation how to use it would be more than welcome then.

I've improved RTBL implementation and added documentation

Thank you, merged.