A "topic" is a collection of related posts. Topics are also called "threads."
A "forum" is a collection of topics.
When you say "forum topic" do you mean forum or topic?
The topic LK linked to allows users to receive notifications when a reply is made to a topic that they have selected.
If you want users to get notified when a user posts a new topic or post to any topic in a forum, that's a bit different.
Kindly ignore the warning LK gave...
At one point ages ago, there was a limit of 200 mails that UBB could send out at once... this was done because the default installation of most versions of the more popular Linux distributions had a /var partition that was simply too small... sending out lots of email caused /var to fill up, which brought down the server. This really isn't something that needs to be worried about anymore, though your host may complain if you do end up sending out lots of mail...
