"Quit sending so many emails!" means he was sending too many emails to people who didn't want them. If every message had value to everyone receiving them, nobody would complain. An unattainable standard. without erring on the side of not sending useful stuff, but you have a decent margin where people will ignore your noise because your signal is valuable. Nobody complains about spam for things they end up buying.

CC'ing a group "just to keep everyone in the loop" is overcommunication. Pulling out the details that are useful for the whole group, if any, and then sending followups with additional details to a subset of people is the effective way to do it. It's a lot of work and it's why so many people who effortlessly handle in-person communication have trouble with written/broadcast patterns, they just aren't used to putting the extra work in.

In my experience, emails from people like this turn into those "Are you sure you want to exit without saving?" pop-up dialogs: if I get them too often, I start ignoring all of them, including the important ones.