If you write !someCommunity@some.instance and aren't on some.instance yourself, that works for everyone, regardless of whether their instance server knows about that community already or not.

If you are on some.instance and write !someCommunity@some.instance, both lemmy and kbin are overzealous and it ends up only working for people on some.instance.

In that case, you can use [link text for lemmy users](/c/someCommunity@some.instance) and [link for kbin users](/search?q=someCommunity@some.instance). The one for kbin users looks a bit different to guarantee the link works even if their instance doesn't have anyone subscribed to someCommunity@some.instance yet. Not sure if the lemmy link works in such a case.````````