The most efficient way to work with email I found is just do it when I need it. I never have my email client open when I am not using email. And when I have it open, I have it set to “manual email fetch” so I cannot see the new ones until I download them at my will.
Anyway, sometimes, you get a question which requires some work to reply. Instead of changing your plans to reply, simply let the other person know when you are going to reply. It is 100 times better to receive short info “no time. will work on it in 3 days” than to wait for any answer for even just 12 hours!
After all, your boss and customers should quickly learn that you might not reply in 3 minutes with half-assed response but you over-deliver if they have just a bit of patience. They will value your input, send their questions sooner and learn to provide a sensible deadline.