Email is great for a lot of things. Creative review isn't one of them. 

The key to getting a creative project completed on time, and within scope is clear communication. When project requirements, deadlines, and details are communicated clearly, there is no confusion over what is expected. This is exactly why in-house creative teams invest in project management & collaboration software, and develop internal tools like creative briefs.

Surprisingly, many of these same teams still rely on email to manage feedback, change requests, and approvals on creative work - a practice that is not only frustrating for creatives and reviewers alike - but also creates delays in getting creative work approved, risking project deadlines (or worse - work is approved for the sake of meeting deadline, and errors are missed).