Hi there! Looks like you linked to a Lemmy community using an URL instead of its name, which doesn't work well for people on different instances. Try fixing it like this: !fediverse@lemmy.ml
Wonder if there is a library that could handle the detection part? I can try and contribute if one doesn't exist
Could also consider persisting the instance software to a local (sqlite?) database to save additional requests whenever a message comes in from a known instance
You need to enable SimplePolicy in your Admin Panel -> expand Settings -> MRF. Type Simple in the top bar and select SimplePolicy, then click save.
Then you add instances from there. However, I would highly recommend you personally vet any actions rather than trust a list maker. Everyone that provides a list has an agenda and it may not be compatible with your own.
Edit: As a side note, I also recommend NormalizeMarkup and AntiLinkSpamPolicy. I also conditionally recommend AntiHellTheadPolicy