>(1) Do I presume correctly that if the WELCOME file gets bounced in this
>manner, that list messages will be bounced also?
 
Yep.
 
>(2) If  the address  is valid as  given, is there  any other  way around
>this?
 
Well, the way to find out whether an address is valid is to try to use it
to write a test  message. If it bounces, it's not valid  :-) So, what you
need to find out now is why it's not valid...
 
  Eric