It would be nice to have the option to aggregate mail alerts into a single mail inside Dimension and/or WSM, with "n minutes" or "as many as x events" as parameter.
It Would reduce the mail clutter a lot.
Most of the items that you can set up notifications for also have reports that can be run that are associated with them. Email notifications are generally for people that'd like instant notification.
What specific alert items are you looking for digests for?
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