This is an old thread, but I recently found the need to send mail to all members of some of the forums I sat up, these forums are used as information center to the boards of associations and does not have many members. The forums is the latest version 2.3.4

A very, very, very simple hack to send mail to all members when new posts or replies are submitted is a tiny change in line 1519 in the file /includes/functions.inc.php from:

  $recipient_result = @mysql_query("SELECT user_name, user_email FROM ".$db_settings['userdata_table']." WHERE user_type > 0 AND new_posting_notification=1", $connid) or raise_error('database_error',mysql_error());

to:

  $recipient_result = @mysql_query("SELECT user_name, user_email FROM ".$db_settings['userdata_table']." WHERE user_type > 0 OR user_lock=0", $connid) or raise_error('database_error',mysql_error());

It works and covers the needs I have, but should be used with caution if the forum has many members!