old_contents: from django.contrib import admin
  
  from email_tracker.models import EmailCategory, TrackedEmail
  
  
  class TrackedEmailAdmin(admin.ModelAdmin):
      list_filter = ('category', )
      readonly_fields = ['subject', 'from_email', 'recipients', 'cc', 'bcc', 'body', 'is_sent', 'category', 'created_at']
      date_hierarchy = 'created_at'
  
  admin.site.register(TrackedEmail, TrackedEmailAdmin)
  admin.site.register(EmailCategory)
  
new_contents: from django.contrib import admin
  
  from email_tracker.models import EmailCategory, TrackedEmail
  
  
  class TrackedEmailAdmin(admin.ModelAdmin):
      list_filter = ('category', 'created_at')
      list_display = ('__unicode__', 'created_at')
      readonly_fields = ['subject', 'from_email', 'recipients', 'cc', 'bcc', 'body', 'is_sent', 'category', 'created_at']
      date_hierarchy = 'created_at'
  
  admin.site.register(TrackedEmail, TrackedEmailAdmin)
  admin.site.register(EmailCategory)
  
subject: Add admin filters and columns