The thread of the bug report I submitted reveals that SDF is not /expressly/ blocking thelemmy.club, at least not transparently. So this leaves these possibilities:

• opaque secret blocking of thelemmy.club perhaps using a firewall
• community-specific blocking that suppresses both Android and mildlyinfuriating
• software defect

After SDF was down for ~9 months, it never fully recovered from the re-opening. So possible there is some obscure software defect related to federating.

If it’s the 1st bullet, I would say it’s likely intentional.. but not necessarily. If, for example, thelemmy.club had a local user with shared IP attacking or annoying SDF in some way, SDF would perhaps block the IP not realising that thelemmy.club uses the same IP.

There is a first for everything. Lemmy users cannot arbitrarily post to unfederated /communities/. To federate to an external community, at least one user on the host (SDF in my case) must subscribe to it. To do that, they must search for it by its full name. IOW, use the search tool to search for something you already know exists. Sometimes it takes a couple attempts because it tries to contact the external host on the spot at that moment. If it finds the community, then the user must subscribe to it. Then they can post there, as well as anyone else on the same host.

Only one person needs to be subscribed. If the first subscriber unsubscribes, then I believe it goes back to the original state of being an unknown (unfederated) community.

The problem in the case at hand is if an SDF user searches for a specific known community hosted by thelemmy.club, that whole host is defederated. So the user-hostile search tool assaults our dignity by outputting no results (instead of doing the dignified diplomatic thing and explain to the user that thelemmy.club is deliberately defederated). In fact, this is a bug. I am reporting it. brb.

(update) Added a bug report:

https://lemmy.sdf.org/post/59309326