There is a visual indication of a complete email addresses: each correct/complete email address is wrapped in a "pill", a light gray one (see OP screenshot). An

There is a visual indication of a complete email addresses: each correct/complete email address is wrapped in a "pill", a light gray one (see OP screenshot). An incomplete email will similarly get wrapped into a dark red pill. Your comment maybe indicates the gray is too subtle, or invisible to users with bad eyesight.