Redmine

I am new to redmine and happened to maintain redmine service in my department.
Our redmine server has been upgrated from so old 0.9.3 to the newest 3.0.1 this week.

Here is a question.
Notification on relation change (adding/deleting related issue) event via email was introduced into 2.4.
Is it possible to disable this notification ?

There could be some aspects to disable; per user, per project or global setting.
Currently I don't find any related item in Administration -> Setting -> Email notifications page.
I already installed Silencer plugin, which disables notification on an update without changing watcher list.
But it affects to updating issue, not adding/deleting related issue.

Any advice will be appreciated.