I've run into this problem a few different times in different circumstances. I have around 200 users who are in SharePoint folders such as SP_Visitors and SP_Contributors. The group is then assigned to a permission level.
I have been trying to create a simple notification workflow that will send an email to all users without me having to add all two hundred email addresses. I've found the SP groups by searching the SharePoint Group option however when I add them to the email area and run the workflow no one gets an email.
I would be grateful for any help.