How do I change or add to the Apple Mail RSS preference to retain messages for three days? The default choices in the pull down menu are 1 day, one week, two weeks, etc. Do I need a terminal command?
From my own testing, it appears that the setting
The GUI settings are "Manually", "after one week", "after two weeks", etc., which appear to correspond to the values 0, 7, 14, etc. It's a reasonable guess that setting it to 3 might make Mail.app delete messages after 3 days.