I agree - that is why I find such general instructions, such as "Answer all Emails immediately", as often emphasized by other "self-optimisation/productivity" articles, so irritating: Emails, as everything else, initially move to the (really long) 'open task list' - as mentioned in the article here. Depending on their importance, they may move to the 'closed-task' list, which is limited in length and sorted by priority. That means two things: a) emails will be answered in descending priority, meaning that some may be answered faster than other and b) some emails have such a low priority to me that I may fail to answer them at all - which is Ok. I have limited time available, so the outcome is if an email isn't important enough there is a chance it won't get answered, and I won't regret it.