my $env = new BerkeleyDB::Env -Flags => DB_CREATE | DB_INIT_CDB |DB_INIT_MPOOL,
  -Home => '/etc/postfix/policydb';
my (%domains);
my $db = tie %domains,"BerkeleyDB::Hash",
  -Filename=> DOMAIN_FILE,
  -Flags=> DB_CREATE,
  -Mode => 0660,
  -Env=> $env
  or syslog 'error', "Can't open DB_File ". DOMAIN_FILE .": $!";

##</code><code>##

  return $domains{$domain} if ($domains{$domain});

##</code><code>##

  # Add to the berkeleydb unless some other process has already done it
  unless($domains{$domain}) {
    my $lock=$db->cds_lock();
    $domains{$domain}=$return;
    $db->db_sync();
    $lock->cds_unlock();
  }