If the user's preference is immediate emails, they will not receive them if they have marked them as read. If the user's preference is daily or weekly, they will still receive them. It does not stop activity from being sent if the user received it VIA push notifications.

Seems like really fine-tuning for the immediate though, because on average there is a `pollingFrequency/numberOfActivityNodes minutes` window after an activity happening that this is really useful.