Forwarding from https://phabricator.wikimedia.org/T624
https://phabricator.wikimedia.org/settings/panel/emailpreferences/ offers a setting for
"A task's subscribers change."
Request is to offer a setting that allows "Do not notify me of changes when the task's subscribers change unless I am reporter of the task", as Bugzilla offers this functionality.
This sounds very specialized.
You can set "A task's subscribers change" to only notify on site or ignore it completely. I'd consider these events to be so low-value that ignoring them is probably reasonable.
Why would an author be interested in the cc list changes, when no comment or other change was made? What's the use-case?
A less specialized tool might be a "super-subscribe" feature - "email me about anything that happens to this task, ignore all my other settings"; I think it can be done today using Herald ("author is me" and "send email").
We're not likely to implement this specific of an option. There will likely someday be an uber-settings page of every notification offered in Phabricator that will let you set email/onsite/never, etc individually for each type - and we'd prefer to solve this issue in a more general/scalable way.
I don't think we're tracking that feature request, so I started a new task and merged this over.
(Self-reminder of the downstream report: https://phabricator.wikimedia.org/T624#2606686 .)