After 8 years of using Redmine I found there is a Rake task for daily e-mail notifications: RedmineReminderEmails
That's really great, even I think this part needs more fine tuning (very sadly, we're PHP company and no one here is Ruby-capable).
Anyway there is an option to list users by their IDs - who will receive notifications.
In would be amazing that this can be set in users preferences, something like: [x] Send me daily e-mail reminder
So every user will check if he/she wants to receive notifications or not.
And of course, there can be configurable default value from this field in redmine config.

I found some plugins for notification emails, but it must be enabled per project / per user, so it's unusable in our scenario.

If someone interested, I have more ideas how to tune this functionality...