Someone pointed me to a recent (15 Feb 2019) New York Times opinion piece by Adam Grant, No, You Can’t Ignore Email. It’s Rude.
Being overwhelmed is no excuse. It’s hard to be good at your job if you’re bad at responding to people.
Reading just the title is sure to generate a response - there are over 500 comments on the article 4 days later - but the details are more nuanced. Adam Grant goes into some of those nuances, but his overall view is that if the message is directed to me directly, I should respond. What he doesn’t say is how fast or even how that response should happen - we all assume that it should be immediately and via email. That is where things go off the rails.
From my perspective, one of the big challenges with email is that it does so many things. I get personal requests for input (business and social), update messages from my family and friends, notices from a variety of services inside and outside the business setting, mailing lists, etc. etc. Happily, spam seems to be handled better and better.
The other challenge is the assumption of how fast and how to respond. My preference is to WAIT and ideally respond in person or via conversation. I am not perfect at this, and sometimes it is fine (and easier) to reply with the information / file being requested. When it gets into a back-and-forth conversation, I tend to drop into a more effective mode of communication (ideally in person, but voice and text tend to get this done faster).
My favorite rule of thumb: To get less email, send less email. Other people will be less inclined to fill my mailbox with replies if I don’t send requests/replies to them in the first place.