Where mail is kept

Postbox keeps captured mail in the database by default. That works almost everywhere, so you can usually skip this page. Read on when you send mail from several processes without a shared database, or want nothing written to disk.

	Database	Memory	Cache
Mail from shells, workers and Celery	yes	no	yes, with Redis or Memcached
Survives a restart	yes	no	depends on the cache
Needs a migration	yes	no	no
Best for	everyday development	quick experiments	servers without the Postbox table

Pick one with POSTBOX_STORAGE:

settings.py

POSTBOX_STORAGE = "django_postbox.storages.DatabaseStorage"  # default

Database #

The default. Mail sent from anywhere that uses your database, runserver, manage.py shell, a Celery worker, all lands in the same inbox and stays there until you clear it.

Memory #

settings.py

POSTBOX_STORAGE = "django_postbox.storages.MemoryStorage"

Mail lives in the memory of one process. It is gone when the process stops, and mail sent from another process, like a Celery worker, never shows up. Good for a quick look, not for daily work.

Cache #

settings.py

POSTBOX_STORAGE = "django_postbox.storages.CacheStorage"
POSTBOX_CACHE = "default"  # an alias from CACHES

Use a shared cache such as Redis or Memcached, and every process sees the same mail without a database table.

Tip

Django’s local-memory cache is per process, just like the memory storage. Use a shared cache backend to get the benefit.

Why the database is the safer choice under load

Django caches cannot list their keys, so the cache storage keeps one index of all mail, guarded by a short lock. When many processes send at the same moment, an entry can get lost, which hides that mail from the inbox. The database storage has no such limit.

Your own storage #

Store mail anywhere else by subclassing django_postbox.storages.BaseStorage and implementing save, messages, get and delete. Then point POSTBOX_STORAGE at your class. Clearing an inbox and the inbox overview build on those four methods, so they work right away.