Hi Michael,
The Reminders popup window is enabled by default in version 11.x. This currently cannot be adjusted. Since it sounds like you'd like to bring back the ability to disable popup reminders, I'll go ahead and change this from a Question to a Proposed Idea so other users can vote up this request as well.
Thanks,
Andrea Free
SmarterTools Inc.
877-357-6278
www.smartertools.com