rand_alpha19 , 7 hours ago

You can search for mags that are already federated but if a community does not appear in a search I’m not even sure if or how a user can create the federated relationship.

On Mbin, if you paste a post from another instance into the search bar, it will fetch that post. Then you can search for the community and subscribe to it. As long as there is at least one subscriber on the instance, it will be federated... eventually.

You can't retroactively fetch previous posts and comments though, you have to manually search for the permalink of each post and comment that occurred before you subscribed. Future stuff should be okay. I had to do this a few weeks ago and I'm pretty sure that's how I managed it.