I was wondering if it is possible to set the options, so all members of the forum get an email as soon as a new topic or an answer to this topic is written?
I have made a forum for our little scout troup, but people forget to check it, and it would therefore be nice, if it could be done automatic.

At the bottom of a thread there is a option watch this topic for replies.
You can click on it & watch the topic.

Alternatively, all users watch the topic they created by default.
Profile>Preferences
Always notify me of replies :Yes

Also, the topics being watched can be added or removed or viewed here.
Profile>Preferences>Topic (s) being watched

Thanks - but that only applies for the topics, they have written themselves or answered in, right?
What I need is more like a "something new has happened on the forum"-email to all members, even when only one post has been written.

Can I as admin on the forum add topics to their watch-list?

You can't really add it to their topic's being watched.

Hmm, so there is no way to draw the member's attention to new topics and posts apart from writing a newsletter each time?

Nopes, there is no way to attain this I am afraid.