Formula fields that are filtered by the context they're viewed in

@danielbmarsh for anybody who reads this, I am linking my answer to your similar three-table scenario, which you had explained. It may help future readers that want to expose the fields of an entity that is only related to the current entity through a middle/junction entity.

Though if you do not need to edit, you should be able to use lookup fields or formulas that return the related entities, such as emails in this case.