Note: This would only be possible to fix for the users that have set the preference "Send me" to the values "A daily summary [...]" or "A weekly summary [...]".
I believe (?) the default is "Individual notifications as they come in", i.e. instant emails and web-notifications sent at the same time.

What @Quiddity says is right, unless we also implement a ~5-minute delay before sending the email. For batched emails, we should definitely be able to prevent emails about read notifications from being sent, but we should look into whether we are doing that already.

I like the idea of a brief delay. I turn off immediate e-mail anyway, but I don't really expect anyone to want separate e-mail messages for multiple related actions (e.g., reverted + talk page message).

I will mentor this task for Google-Code-in-2019

Imported into GCI site as https://codein.withgoogle.com/tasks/5918609558208510/

Change 556089 had a related patch set uploaded (by IAmNetx; owner: IAmNetx):
[mediawiki/extensions/Echo@master] Add preference to not receive digests about read notifications

https://gerrit.wikimedia.org/r/556089

Change 556089 merged by jenkins-bot:
[mediawiki/extensions/Echo@master] Add preference to not receive digests about read notifications

https://gerrit.wikimedia.org/r/556089

I think this can be announced in tech news (maybe with a special thanks to our GCI student, if appropriate). It should be on wmf.11 next week.

It is adding a new preference under the "email frequency" option on Special:Preferences#notifications. Default behavior is unchanged.

@Etonkovidova Could you take a look and resolve as appropriate? Thanks!

In T169386#5736072, @SBisson wrote:

@Etonkovidova Could you take a look and resolve as appropriate? Thanks!

Re-opeing the task - some additional testing is needed - it seems there is a discrepancy between what notifications Special:Notifications page displays as Unread and what an email lists as unread,

I'd be satisfied by these outcomes. Just reducing the unnecessary e-mail would help me.