Right now, individual emails are sent every time a project item is updated in any way. With projects that have cascading dates enabled and many predecessor/successor relationships, one schedule change can lead to several downstream changes which all in turn send out emails.
I would suggest the option of having certain email notification types (like changes in scheduling, assignment, etc.) to be sent as a daily/weekly digest. That way, as a project contributor/manager, instead of receiving many emails as a project is being updated, you would get a summary of the changes made that day.
For scheduling changes, it may make more sense to send out a summary of daily changes that have the latest change. This means if a project is going through a re-baselining and dates/times are being changed frequently during a single day, the person those tasks are assigned to would get a summary with the latest date that was set
