It is about this below option, is it? If you activate this, you get emails for all updates of your bundle purchases.
But unlike following, you cannot de-activate purchase-notifications preemptivly per case basis.
At least you do can deactivate it per case, when getting the mail. But I wonder, how would you re-activate the mails for a project? I only ever saw the follow button and that is for accounts and not for projects.
So maybe I misunderstand something?