## tested now (had the sort backwards)
my %domain;
foreach my $address (@addresses) {
  my ($name, $host) = split(/\@/, $address);
  push @{$domain{$host}},$address
}
foreach my $host (sort { $#{$domain{$b}} <=> $#{$domain{$a}} } keys %domain) {
  mailout(@{$domain{$host}});
}