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![](https://lemmy.world/pictrs/image/0943eca5-c4c2-4d65-acc2-7e220598f99e.png)
The first time anybody on your instance searches for a separate lemmy community, your Lemmy instance reaches out for the other community and learns that it exists. After that point it shows up in searches and after one person subscribes it appears in your instance’s All feed.
I’m more certain about the first search part.