The default value is "Auto-Delete= No" for lists with "Validate= All" and
"Auto-Delete= Yes,Semi-Auto,Delay(4),Max(100)" for other lists.

Per the manuals :)  Although actually I need to make a change because
"Auto-Delete=" first appeared in 1.7f, before the big changes to the
Validate= keyword.  So where it says "Validate= All" above we should
change that to read '"Validate= Yes" or higher'.  So the bottom line is
that Auto-Delete is turned off by default unless you have "Validate= No".

Nathan