Sending mail to detailed groups? Ok, I need a bit of help with this one.

I have a website where I created a newsletter using Simplenews - works just fine, I'm sending some welcoming text + attached views of new things on site. But now I need to make something more with it.

I want to create new type of newsletter, that would be sent irregularly - or manualy as some would say. That is not a problem. Question appears here: I want admin to be able to create groups of users (manually again adding mails to the group etc.) for example, let's say I want to have two new groups for start:


group a
group b


And from time to time, admin needs to send a mail to all the email addresses in the selected group. How can I achieve that? Is even Simplenews a good idea in this situation? Or maybe there's some better tool? 

Thanks in advance
I guess Simplenews Roles modules can help you for creating the groups.

You can assign users to a specific role and then based on this roles you can send Simplenews.

For Eg.

User 1 and User 2 can be assigned to role A

And

User 3 and User 4 can be assigned to role B

Now you can use role A and B for sending Simplenews.

I guess this helps.