Hi on request of the moderator now in the right Forum:
sending emails to user groups (only) by the Moderator (or Admin) is usefull for me when doing projects. For now I found a separate plugin called 'Email Users' that could be of help. However when this would work from within the Simple:Press forum you could mail a subgroup (e.g. those who did not login for a while, those who only participated in 2 of the 20 topics etc.). Maybe it is important to explain that I want to use the platform for projects that only last 3 days to 2 weeks or so.