> I have added another owner to the header. Must he establish his own password or
> must he know mine?
 
The list password is separate from the personal passwords, although all
can be used to administer a list (if you are a list-owner).  No user or
list-owner is able to use another person's personal password, and it's
probably a good practise not to share them.  It's strongly advisable for
your co-owner to establish a personal password so that a hacker cannot
forge his identity and then try to control your list.
 
-- Roger Burns    [log in to unmask]