If you've found yourself in a shared box and can't access a message or thread, that means the owner has restricted your access to it. You won't see a read-only view, and will have to request access in order to view the hidden messages.
After you're granted access to the thread, you still won't be able to respond, but you will have read-only access.
How will I know I have access to a thread after requesting access from the owner?
Streak first sends a request to the message owner. If there are multiple owners, they'll all receive a request. If any owner grants access, Streak will send you an email notifying you that you've been granted access.
Here's what that looks like for Adriana (owner of the thread) and Andrew (requester) -
Andrew requests access:
Adriana is notified Andrew is requesting access via email:
Adriana navigates to thread to confirm she wants to give access:
Andrew receives a notification that he can now access the thread: