Hi again Amy,
Thanks for pointing the DisplayDate_1 variable out. It was not what I was looking for (my first description was a bit unclear) but it was close! :-)
I looked into all the views, they have a "Date" column, and in this column properties unselect "Display abbreviated date" and now it is solved!
Again thanks for pointing me in the right direction, I will now mark this topic as solved.
PS I created a master template where INBOX, SENT, ALL DOCUMENTS etc have the "full" date format. But how to get this into users customized folders, because they still have old date....
PS2 load convert -u mail\username * mail9templatename does indeed inherit from #INBOX-folder design and date format. That means that all folders are also fixed. Problem totally solved!