sub notify_users {
    my $message = shift;

    # Get the list of addresses to notify
    my @addr = @{$dbh -> selectall_arrayref(q[
        SELECT addr
        FROM email,
             (SELECT userid
              FROM usernames
              WHERE 0 <> position(lower(username) IN ?)
                AND userid <> ?
              EXCEPT
              SELECT userid
              FROM ignore
              WHERE ignore_userid = ?) ids
        WHERE email.userid = ids.userid],
        undef,
        lc $message -> {'message'},
        $message -> {'userid'},
        $message -> {'userid'})};

    # flatten the array
    $_ = $_ -> [0] for @addr;
    @addr = grep length(), @addr;
    return unless @addr;

    ....

}