code: def get_users_by_email(cls, emails):
          
          users = User.objects.filter(email__in=emails)
          present_emails = users.values_list('email', flat=True)
          missing_emails = list(set(emails) - set(present_emails))
          return users, missing_emails
docs: Accept a list of emails, and separate them into users that exist on OpenEdX and users who don't.
  
          Args:
              emails: An iterable of email addresses to split between existing and nonexisting
  
          Returns:
              users: Queryset of users who exist in the OpenEdX platform and who were in the list of email addresses
              missing_emails: List of unique emails which were in the original list, but do not yet exist as users