You hear often, that email is broken - and a magical software tool is going to solve it. I don’t think so. But you can solve it. Here is a great guide from Harvard Business Review.
Key take aways:
Write the necessary action in the subject. Example: ACTION, DECISION, SIGN, INFO. I love it, especially as you can categorise and prioritise automatically based on those classifications.
Write an executive summary in one sentence in the beginning of an email.
Include relevant background information as bullet points, which helps to fly through those fast.