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. 

I suspect the nearest we can offer - out of the box - is the private messaging plugin. This does allow you to send a PM (and potentially an email notification of the PM) to all users in a specific user group.

We do not have an email application as such I am afraid.

OK, no problem. Just a thought (however I am not a developper)... maybe the Announce plugin could have an option to do this. 

announce plugin is for posting an announcement in the forum...  just as easy to send a pm (maybe easier) to usergroups than it would be when making an announcement (UI wise and maybe code)...

but your request has been noted...

PM's (and announce) are only read by the users when the user group visits the forum (unless they subscribe to a announce topic). I need a tool to reach them also when they did not visit the forum or subscribed.  

They will be notified by email that there is a PM to read however - although they can opt out of this in their forum profile settings.

I honestly do not know of there are any WP email plugins available that can take a custom database query to determine recipients but it might be worth taking a look for one...

I guess I would add that if you want a custom plugin for emailing message directly to usergroups, you could use our custom plugin service...  we could give you a quote to develop this for you...  

this is our first request for something like this so its frankly, quite low on our priority list...

Yellow Swordfish said
They will be notified by email that there is a PM to read however - although they can opt out of this in their forum profile settings.
I honestly do not know of there are any WP email plugins available that can take a custom database query to determine recipients but it might be worth taking a look for one...

So the standard setting here is ON and users will receive the email that a PM there to read?:  Help text: "If enabled, users may choose to enable or disable emails for themselves in their profile".

yes - as I said above.