sub lookup {
  die unless wantarray; # call me in list context only
  my $item = shift;
  return values %{$EMail{$item}} if exists $EMail{$item}; # category name
  for my $cat (keys %EMail) {
    return $EMail{$cat}{$item} if exists $EMail{$cat}{$item}; # single name
  }
  return; # not found
}
sub GetEmailFor {
  my @results = map { lookup($_) } @_;
  return join ",", @results;
}

##</code><code>##

use Memoize;
memoize('lookup');
sub I_have_changed_EMail {
  unmemoize('lookup');
  memoize('lookup');
}