I just came across a great article on slowing down the amount of emails we get to a regular work schedule. Basecamp implemented the 'Work Can Wait' feature : https://basecamp.com/3/work-can-wait
You can schedule when you want to receive messages.. which I suspect is probably not a super tricky thing to add into the user profile. Then when the cron runs to send out emails just verify it's not during the 'quiet' time they have setup.
What do you folks think?