Edit: Okay, so I tried to reproduce this while I was putting together a bug report, and it's no longer doing it when I was following my "steps to reproduce". I re-added .ml to my domain filter list, and can still resolve posts to c/Books which has a link to .ml in its description. So maybe it was just a glitch? I'm gonna play around with it and see before submitting it as a bug. But I do know before I removed .ml from that list yesterday, it refused to because of the link in the description (none of the test posts hit on that domain) and consistently said Domain is blocked. :sigh:

Edit 2: Ok, now it's behaving as described. There must be some lag/delay between adding a domain to the filter list and it applying to inbound federation. Submitting a bug.

Edit 3: Bug 6320

I was one of the trailblazers who defeded from .ml and once the domain filtering feature was added, I added lemmy [dot] ml to my domain blocks in the admin panel. Reason being, I don't want .ml content including crossposts and re-posted images.

I thought that was working great until I noticed today that I hadn't gotten any posts to !books@lemmy.world for several months. Even trying to manually resolve a post pulled from there directly, it wouldn't load. Finally checked the server logs, and there was a Domain is blocked event right after the logged call to ResolveObject. Of course the logs didn't say what domain.

Long story short, after scouring the randomly-selected test post to see if there was some kind of false positive, I finally realize there's a "Related Community" link to a community on .ml in c/Books's community description and that was what it was hitting on. Any post coming in to c/Books was being rejected because the community description linked to something in my site's URL filters.