Microsoft Outlook is a web-based suite of webmail, contacts, tasks, and calendaring services.
Your reviewer gets the current image or PDF and a clear question. Your review card shows which revision you sent.
Your reviewer gets the current proof and a clear decision deadline by email when a card is ready for review.
Your maker gets a rework email that names the reviewed proof and fixes due next.
Your reviewers find campaign drafts right on their review tasks. A comment shows which version came from email.