Brilliant email etiquette implies that we acknowledge emails within an acceptable time frame (at least those which need an answer). For those emails which you know a substantive and proper reply is needed than plan the necessary work into your work schedule. They key is to manage their expectation whilst not putting undue pressure on yourself. Decide when you can reasonably make a proper reply and let the recipient know.
Simply tell them when you will reply but don’t add a line saying ‘ is this OK’. First, this leaves the door open for the sender to change your priorities. They will soon say if it’s not OK. Second, its asking for at least another round of unnecessary email ping-pong as the sender says ‘OK’ and you feel compelled to email back again.
Once you’ve acknowledged the email and planned when to deal with it make sure you keep track of the actions you need to take and also the email itself. You gaol should be to handle each email once and not have to keep looking for those ones which still need attention.
Implement a process which enable you to find it easily. For example, file it, place it in a pending folder or create a task from it. Choose a way which suites your way of working and managing your day.