Sending mail to detailed groups?
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.