Pause for a moment before replying and ask:
This is process-centric approach to e-mail. Think for a minute or two on how to get from the current state to a desired outcome with a minimum number of messages. Finally, write a reply which clearly describes the process and where we stand. Also use this for writing from scratch.
Process-centric approach reduces the number of emails in your inbox and closes the loop.
Less mental clutter = more resources for deep thinking.
Make it your default behavior. It's sender's responsibility to convince you to reply. Do not reply if:
Most every day of most every week I was pushing my mind to grapple with results of consequence, regardless if there was a deadline. I solved proofs in the subway and when shoveling snow.