There is not an admin function for that, and I do not control individual users logins, and I do not want to go and do that for every user if I could.
misago authors suggests
In the short term If everyone could go to 'Forum option' in their user panel, and remove notify by email unless they specifically require it, it would help in the interim.
A big problem is that users who are not logged in, but have featured in threads (almost everyone) are still potentially racking up email notifications).
The misago author has put disabling email notifications as an admin function on the roadmap, and this will be the ultimate solution.