How can you configure ACLs for MageMail?
The MageMail configuration settings are within the Newsletter configuration settings page. This simplifies initial installation (no dreaded 404 upon initial installation) and is also a nice logical location for them. There is also an AJAX controller which is a custom adminhtml controller in the MageMail module. That controller also (as of July 10) relies upon the newsletter ACL for access.
In order to control access to the MageMail configuration, you'll want to use the Configuration > Newsletter resource in the role resources:
Side note: 99.9% of the time, the person installing the extension is a super admin, and sub-admin user roles don't need access to the MageMail configuration on a day-to-day basis - so there shouldn't be an urgent need to update the extension due to the _isAllowed() issue with SUPEE-6285 issue, but it's available if you need it.