The cosmos encapsulates all reality. If it exists, it is within the cosmos. To say that something comes from “beyond the cosmos” is a contradiction in terms.
There are four “layers” to the cosmos. The outermost layer are the Realms of the Gods. The Old Gods resided here, and Mithral, Vorpal, Dominus, and Covenant were forbidden by Neutral from ever leaving them. Most of the New Gods live here as well. The planes are extremely morphic and respond easily to the will of powerful Outsiders. The Realms of the Gods are Mechanus, Bytopia, Celestia, Arcadia, Elysium, the Beastlands, Arborea, Ysgard, Limbo, Pandemonium, Gehenna, the Abyss, Hades, Hell, Carceri, Acheron, and the Outlands.
The next layer are the Elemental Planes. This includes the four Primary Elemental Planes of Fire, Water, Air, and Earth, as well as the Positive and Negative Energy Plane, as well as the twelve demi-planes where they mix with one another. These planes provide the stability and consistency of the Prime.
The next layer inside are the Transient Planes, mostly the Ethereal and the Shadow Plane, which are reflections of the Prime squeezed in between the Elemental Planes and the Prime, created and sustained as a side effect of the use of magic. Between all of the planes, a sort of soup which the lot of them float within, is the Astral Plane. Though its portals lead to all planes, it physically connects to none of them, and thus it is often considered a Transient Plane.
Finally, at the heart of it all, is the Prime Material Plane. No one can be summoned from the Prime, and you can only summon others from the Prime, making it prime real estate (no pun intended). However, due to the compacts of gods Old and New, it is very difficult for Outsiders to invade the Prime of their own volition.