Are there any tools available in the Admin client that will easily enable me to determine the date a mail file was last opened by it’s owner?
Subject: no but take a look at user activity
you can use the user activity to get this info. If you do a google search for UserActivity you can find a class that was created to get to this info using LotusScript. I would guess you are looking for a way to find out what mail files have not been used in xx days? Take a look in openntf.org, you might find something there. Also take a look on helpsoft.com, they have a utility called database activity that will do what you want.
Subject: Activity Trends
Have you setup Activity Trends?