Spending an hour or more writing an email is rare. If it’s well-written with valuable information, it should be acknowledged immediately.
Something simple is all that’s needed. “Hey, received your email. Looks super comprehensive. Will get back to you with my thoughts. Thx!”
Many people star emails in their inbox so they can read it later and prepare a thorough reply. However, the sender doesn’t know this and they could feel ignored or discouraged.
Top business leaders know the importance of a quick short reply. Be like them.