I was just trying this myself but not as a external island.
As a guest on ver 7.4.2
Permission setting for guests
Can see shout box=0
No display (Okay)
Can see shout box=1
Can see display(Okay)
All okay so far. But here is the rub.
Can use shout box=0
Get a pop up message denied(Okay)
can use shout box=1
When you try to post you get a message sending.
But the shout does not appear in the island.(Not Okay)
