What sends notifications
One capability in the whole suite sends notifications: Approval. Nothing else emails or messages anyone.
The second thing to know is that email and Slack are not alternatives. For the same event, both go out.
#Channels

Email, sent from a Capable address with Reply-To set to the person who requested the approval
Slack direct messages to individuals, matched to their Confluence email address
Slack channel broadcasts, configured per Confluence space by an administrator
#What triggers one
Approval request from someone for a page
Someone added you as an approver on a page
A page has been updated and requires your approval
An approver approved, rejected or commented on a request (optionally with a comment)
A page has been approved
A page has been rejected
Your approval for a page has expired
Watchers are set per space, up to 50 people, and are notified on status changes. That is how people who are not approvers stay informed.
#A few things worth knowing
If nothing in your site uses Approval, nobody will ever receive a Capable notification.
Email comes from a Capable address with Reply-To set to whoever requested the approval, so replying reaches a person.
Turning off email does not turn off Slack.
#Related
Approval only. Both channels, same event.
