When someone we need an answer from does not reply our email, it is convenient to just wait for an answer. After all, we have it on black and white. It’s there in the cyber forest, somewhere. It’s the responsibility of the recipient to reply us.
Meanwhile things get delayed. When that happens it does not matter if it is because you did not receive a reply, it is someone else’s fault.
Your role is to keep the project moving. That’s your responsibility.
Pick up the phone and call. Call till you get a firm answer to move your project forward.