Comment 13 for bug 46237

+1 for not notifying duplication events by default. This happens frequently in GNOME bugzilla and there is always angry email returned. I would be very skeptical if any of the bug subscribers are even interested in the fact that duplicates are being reported anyway - if the duplicates contain any useful information then this is normally added to the parent bug in a comment and everyone is notified of this.

There is some value in developers/maintainers being notified of duplicates and this class of user can be expected to have a mail sorting scheme to handle the traffic. I'd recommend an opt-in option for duplication events.

In my experience I like being notified of duplicates on things I am maintaining and duplicate notices I get for bugs I filed 2 years ago I don't want to be notified about.