I think our norms around email could be based to some extent on very old norms from ancient tribal culture - there you had to respond, and not just weeks later, if someone asked you about something. Therefore one would have to target one of the things you mentioned (length, cost, permancence).
What if we had an email-tax, thereby changing the cost of the form? (Not so easy to implement in practice, of course). That would not change the norms per se but it would reduce the burden of the norms that result from a mismatch between the evolutionary source of the norms and the current technical environment. What email-tax level would lead to the highest welfare (happiness, productivity) could be an empirical question then (and I think the optimal tax would be higher than zero).
And the rarer strategy of actually dealing with all of one’s emails promptly doesn’t even seem obviously better.
Why not?
I get lost there, because my model is 'emails are important for communication, they have the problems you describe here, and the solution is to answer as quickly as possible'.
Sometimes, responding takes too much effort for that to be reasonable, but it often doesn't.
At work, I'm cc'd on maybe 100-200 emails daily, and some of my coworkers get many times more. Many of those are unimportant (or rather, I'm on a thread that someone else is mainly handling, so they're unimportant *for me*), but it isn't normally easy to tell which (and many of those could become important for me at any time). And when it is important, responding often requires reading a lengthy message chain I got added to in the middle. I try to scan through them quickly once a day, and thoroughly every 2-3 days. Most I never respond to because it's not needed.
At my personal email address, I also get 100-200 emails daily. Most of them are unimportant, but continue to arrive no matter how many times I unsubscribe from various lists or try to use filters to block them. Most of the rest are auto-generated, like order and shipment notifications. I find sorting through those to find the few important ones annoying, and it's easier and faster for me to do it in larger batches, say once every two weeks. Anyone who really needs me urgently is more likely to reach me by text, phone, or another messaging platform.
I think the norms follow from quite ancient communication expectations. If someone in your village sends their child with a request, you can say no, but you can't just ignore it. Acknowledgement is a near-requirement for communication to have actually happened.
What has changed is the number of people who expect to communicate with you, and the ease of doing so. Which leads to a lot of things that look like communication, but aren't. e-mails run the gamut from personal messages from a close friend or relative (which you may damage the relationship by failing to respond appropriately, but which you can negotiate expectations over time) to automated spam which you probably automatically discard.
The ones in-between, from strangers or distant acquaintances are the tricky ones. You don't necessarily owe them anything, but they might have something useful to say, and a few of them might turn into closer friends. So you have to decide how much to invest, from a boilerplate "thanks for the e-mail, I probably won't have time to read it thoroughly." to an actual thoughtful engagement.
Celebrities have had to deal with this by mail (and telegram) for a century. Some have hired people to respond for them. Some are famous for personal responses. Some are black holes. There is reputational impact to those choices, but they're all acceptable.
What about a norm that emails should only require one reply, and almost never end up as long email chains? I think most emails that I receive are parts of long threads, such as threads to schedule a date and time for a meeting, or threads to discuss technical information. Shortening those threads by being more direct or switching the conversation to a better medium (like a call) seems like a worthwhile goal.
Cal Newport calls this a process-centric approach, in which one spends time up front writing emails and replies that do not require much or any follow-up. For example, instead of discussing a complex idea over email, Newport would argue that one should just schedule a call. Likewise, Newport has a template that allows for meetings to get scheduled with just two replies (shown in the linked source). Newport argues that although this approach reduces the number of times one must check one's inbox per day, it does not reduce the total time spent reading and writing emails. However, I suspect that if both the sender and receiver held this approach as a norm, the total time spent on email might decrease, because one would receive emails that are already easy to resolve.
It seems like this approach could be a norm that could plausibly spread because it confers a clear benefit but only requires one to write emails a bit differently. If enough people adopt it, the number of emails sent and received would decrease. In contrast, strategies like charging people to send one emails or not responding to emails by default seem tenable only for those who work independently of any typical employer, so they are unlikely to spread.
This approach depends on at least one side knowing that the chain will likely be long (not necessarily obvious, and usually untrue at work for me), and for it being feasible to quickly schedule a short call with the relevant parties (ditto, due to time zone issues plus already-complex schedules).
There seems to be a common phenomenon where people get messages, then fail to respond to them, then feel bad. And the rarer strategy of actually dealing with all of one’s emails promptly doesn’t even seem obviously better. Was that how things were with letters or telegrams? Is it just that there are so many messages now, because they are easy to send?
Could email, say, have gone a different way?
I act as though I’m assuming email involves implied norms, though I didn’t agree to them. For instance, if someone writes me a personal message, I think I should not delete it without reading it, unless they deserve my disregard for some reason. If someone sends me a message asking me to do something, I act like I think I should do it in a timely fashion, if it is a reasonable request. If I write to someone, I feel like I should make it less terse than ‘ok.’. At least, many people seem to constantly feel bad for failing to uphold some standards that are I guess implicitly bought into by having an email address. (And not having an email address would be pretty wild.)
Was this bad luck, and we could instead have developed happier norms? For instance, that there is no expectation that one read emails, or that responding in about a month is proper, or that tersity is expected, like text messages? Or the norm that you are meant to respond within a few seconds, or consider it dead, like verbal speech? Or the norm where if you want to put something in someone else’s to-do list, you find a slot in their Calendly and send them money for it? My guess is no - the norms are mostly implied by the length and cost and permanence of the form. Could we have a form that better implies happier norms in that case?