_expand_hostname =head2 _expand_address

     Usage     : @expanded = _expand_ip($ip); # For example
     Returns   : Given an ip, hostname, or e-mail address, it will expand
                 that into the "appropriate lookups" which sendmail would use
                 (e.g., given '192.168.1.2', _expand_ip would return
                 192.168.1.2, 192.168.1, 192.168, and 192)
     Argument  : The IP Address, hostname, or e-mail address to expand
     Throws    : 
     Comments  : 
     See Also  :