You might try submitting a support ticket. I needed to know awhile ago who made changes to our global email notifications and support was able pull who and when for me.
Turned out to be someone who was going on maternity leave and didn't want to come back to a ton of notificaiton emails but forgot to go into their own profile and went to Setup instead! We were laughing about it again just lask week. After 4 years in Workfront, it turned out to be a good time to review which notifications we really use anyway. :)