Group email notifications to one email per specified period of time
when having an attack or something - getting 1 email for every change is too much... you should allow a way to group emails together. this also reduce the number of emails sents using the user email box so it won't be block or something

Email limiting was introduced in v2.9.9.9. This allows you to throttle the number of emails sent over a given period of time.
Emails generated after the limit is reached are not sent, this is ideal for notification type emails. This can be extended to group generated emails until the cool-down period has passed and send in a single batch if required although existing rules/functionality already caters for this.
The event count rule is also flexible enough to send in batches of X and then the final email a few minutes later if the count is not reached ensuring you do not miss any events. The inactivity rule already sends in batches but will not be instant which is required to detect an attack of some kind.
My suggestion would be to setup multiple configurations for critical directories like this. One that sends batched emails after a period of inactivity, and another that sends a notification email when something changes but limited to one every hour or so.
Original limit idea: https://deventerprise.uservoice.com/forums/198724-general/suggestions/7087700-limit-number-of-emails-that-can-be-sent-in-a-time