Context...
a player had a humonculus familiar outside of the sphere, the bbeg grabs him, he cast resilient sphere on himself. there you go, he's free...
now the player ask the DM... wait a minute, can i cast a touch spell and have my familiar deliver it ?

DM looks at the familiar, familiar can deliver a touch spell instead of the player.
DM looks at resilient sphere... nothing says anything about familiars not able to deliver touch spells.
but... resilient sphere does say nothing gets in or out.

DM temporary ruling: no you still cast the spell and now has to send it to your familiar, but can't because of the sphere.
DM wonders: how would other people have voted this ?

so here i am, wondering if my decision was right or wrong. did i just deny a cool trick from my player, or was it the right call ?

Resilient Sphere says:

Nothing--not physical objects, energy, or other spell effects--can pass through the barrier

And Find Familiar says:

Finally, when you cast a spell with a range of touch, your familiar can deliver the spell as if it had cast the spell

Seeing as the familiar can deliver the spell as if it had cast it, the spell effect isn't passing through the barrier, it's being treated as if it originated from within the barrier. Therefore RAW the spell could be cast by the familiar.

Interesting from the familiar spell. 

he's an artificer and the humonculus comes from his infusion though and the text is different.
i'm guessing it comes back to the same thing, but i will show it anyway, just in case.

Reactions

Channel Magic. The homunculus delivers a spell you cast that has a range of touch. The homunculus must be within 120 feet of you.

this begged me the question, how can the spell cast by the player get to the humonculous ?
i'm also leaning toward the "it works" thing, just curious about the physics of it.

I think the problem here is taking the "nothing - can pass through the barrier" thing too literally. Obviously, light and sound pass through the barrier or you would be Blinded or Deafened. Telepathy is probably not blocked. Since it is never described exactly how the energy of the spell transfers from you to your familiar, you could just say it just pops out of existence and reforms at your familiar.

The sphere is immune to all damage, and a creature or object inside can't be damaged by attacks or effects originating from outside, nor can a creature inside the sphere damage anything outside it.

To play Devil's Advocate to my own opinion, however, I offer this. It also is possible to preserve your original ruling if you take this line and have it apply to proxies, which your familiar would be. Let's be clear, you are casting the spell and if you aren't allowed to affect things outside the sphere, you can rule that the attempt fails. That would be a pretty strict ruling but, not too unfair considering you made yourself untouchable.

Quote from Wtfdndad >>

I think the problem here is taking the "nothing - can pass through the barrier" thing too literally. Obviously, light and sound pass through the barrier or you would be Blinded or Deafened. Telepathy is probably not blocked. Since it is never described exactly how the energy of the spell transfers from you to your familiar, you could just say it just pops out of existence and reforms at your familiar.

The sphere is immune to all damage, and a creature or object inside can't be damaged by attacks or effects originating from outside, nor can a creature inside the sphere damage anything outside it.

 

To play Devil's Advocate to my own opinion, however, I offer this. It also is possible to preserve your original ruling if you take this line and have it apply to proxies, which your familiar would be. Let's be clear, you are casting the spell and if you aren't allowed to affect things outside the sphere, you can rule that the attempt fails. That would be a pretty strict ruling but, not too unfair considering you made yourself untouchable.

 Who said anything about not taking it too literal. In my games the bubble is transparent so he can see outside. But air sounds and everything else doesnt get in or out.

Latest Sage Advice (v2.5) update has a new entry:

If you are affecting a target with telekinesis and an ally put you inside Otiluke’s resilient sphere, can you continue affecting the target or other targets with the existing telekinesis spell? You can maintain your telekinetic grip on a target you were already affecting, but you can’t affect a new target. The sphere provides total cover that stops you from targeting anything outside it.

This provides some clarification about RAI.

The sphere's total cover blocks the targeting, but not an existing control. So telepathy would work?

I suspect the issue with spell casting is that the spell is being cast INSIDE the sphere, whereas the familiar is outside the sphere, so does the targeting block occur?

Google search pointed me to another thread on the same topic: https://www.dndbeyond.com/forums/dungeons-dragons-discussion/rules-game-mechanics/53742-warlock-stuck-in-resilient-sphere