To view Distribution Groups a user is in, as well as their Pushpage Job History:
  1. Navigate to Core.
  2. Select Users/Access > Profile > Edit User Profile Data.
  3. Search/select your user.
  4. Scroll down on the right to E-Mail Notifications.
This will list the Distribution Groups a user is part of. If a box to the left of a group is un-checked, it means the user has opted out of receiving emails from this group.