yes it is annoying but this is not the matter of developer
if admin/mod subscribes to all board of forums
forum is getting running on a server with no email limit problem or admin have to get it fixed on there own part
admin/mod/users are willing to see 1000000000 new emails today even they go into junk or inbox.
they set notify for all board of forumss by mistake and now they want to get rid of it
they can unnotify all boards at once as they turned it on