As a consequences of a forum software upgrade, and enhanced functionality in the notifications system: Huston, we have a problem.
All users have inherited notify absolutely fucking everything by email.
This is causing an email flood, that nobody wants (probably).
In the short term If everyone could please go to 'Forum option' in their user panel and remove notify by email for all cases, unless they specifically require it in certain cases, it would massively help in the interim ('notify on site' is the preferred setting, and will allow the site notifications to track activity and give you return links to specific activity).
Hopefully a more permanent solution will follow.
Note, having made the selections you may have to scroll down in the Forum Options page to reveal the "save" button. If you don't save the changes, they will revert when you leave the page.
----edit----
I have applied a patch that now sets all existing users 'Forum Option' to default to 'notify to site' rather than 'notify to site and email'.
Could users please check their settings, and that they are indeed not notifying by email by default?