django-email-relay

django-email-relay enables Django projects without direct access to a preferred SMTP server to use that server for email dispatch.

It consists of two parts:

1. A Django app with a custom email backend that stores emails in a central database queue. This is what you will use on all the distributed Django projects that you would like to give access to the preferred SMTP server.

2. A relay service that reads from this queue to orchestrate email sending. It is available as either a standalone Docker image or a management command to be used within a Django project that does have access to the preferred SMTP server.

Why?

Okay, so why opt for this setup? A few reasons:

• The potential for emails sent through an external Email Service Provider (ESP) to be marked as spam or filtered, a common issue when routing transactional emails from internal applications to internal users via an ESP.
• It eliminates the necessity to open firewall ports or the need to utilize services like Tailscale for SMTP server access.
• It decouples the emailing process from the main web application, much in the same way as using a task queue like Celery or Django-Q2 would.

Requirements

• Python 3.8, 3.9, 3.10, 3.11, or 3.12
• Django 3.2, 4.1, or 4.2
• PostgreSQL (for provided Docker image)

Installation

Relay Service

Django App

1. Install the package from PyPI:

pip install django-email-relay

2. Add email_relay to your INSTALLED_APPS setting:

INSTALLED_APPS = [
    # ...
    "email_relay",
    # ...
]

3. Add the RelayDatabaseEmailBackend to your EMAIL_BACKEND setting:

EMAIL_BACKEND = "email_relay.backend.RelayDatabaseEmailBackend"

4. Add the email relay database to your DATABASES setting. A default database alias is pfrom email_relay.conf import EMAIL_RELAY_DATABASE_ALIAS:

from email_relay.conf import EMAIL_RELAY_DATABASE_ALIAS

DATABASES = {
    # ...
    EMAIL_RELAY_DATABASE_ALIAS: {
        "ENGINE": "django.db.backends.postgresql",
        "NAME": "email_relay_db",
        "USER": "email_relay_user",
        "PASSWORD": "email_relay_password",
        "HOST": "localhost",
        "PORT": "5432",
    },
    # ...
}

If you would like to use a different database alias, you will also need to set the DATABASE_ALIAS setting within your DJANGO_EMAIL_RELAY settings:

DATABASES = {
    # ...
    "some_alias": {
        "ENGINE": "django.db.backends.postgresql",
        "NAME": "email_relay_db",
        "USER": "email_relay_user",
        "PASSWORD": "email_relay_password",
        "HOST": "localhost",
        "PORT": "5432",
    },
    # ...
}

DJANGO_EMAIL_RELAY = {
    # ...
    "DATABASE_ALIAS": "some_alias",
    # ...
}

4. Add the EmailDatabaseRouter to your DATABASE_ROUTERS setting:

DATABASE_ROUTERS = [
    # ...
    "email_relay.db.EmailDatabaseRouter",
    # ...
]

Usage

Configuration

Relay Service

Configuration of the relay service differs depending on whether you are using the provided Docker image or the management command within a Django project.

Docker

When running the relay service using Docker, config values are set via environment variables. The names of the environment variables are the same as the Django settings, e.g. to set DEBUG to True, you would set -e "DEBUG=True" when running the container.

For settings that are dictionaries, a __ is used to separate the keys, e.g. to set DATABASES["default"]["CONN_MAX_AGE"] to 600 or 10 minutes, you would set -e "DATABASES__default__CONN_MAX_AGE=600".

Django

When running the relay service from a Django project, config values are read from the Django settings for that project.

Django App

Configuration of the Django app is done through the DJANGO_EMAIL_RELAY dictionary in your Django settings. All settings are optional. Here is an example configuration, with the default values shown:

DJANGO_EMAIL_RELAY = {
    "DATABASE_ALIAS": email_relay.conf.EMAIL_RELAY_DATABASE_ALIAS,  # "email_relay_db"
    "EMAIL_MAX_BATCH": None,
    "EMAIL_MAX_DEFERRED": None,
    "EMAIL_MAX_RETRIES": None,
    "EMPTY_QUEUE_SLEEP": 30,
    "EMAIL_THROTTLE": 0,
    "MESSAGES_BATCH_SIZE": None,
}

DATABASE_ALIAS

The database alias to use for the email relay database. This must match the database alias used in your DATABASES setting. A default is provided at email_relay.conf.EMAIL_RELAY_DATABASE_ALIAS. You should only need to set this if you are using a different database alias.

EMAIL_MAX_BATCH

The maximum number of emails to send in a single batch. The default is None, which means there is no limit.

EMAIL_MAX_DEFERRED

The maximum number of emails that can be deferred before the relay service stops sending emails. The default is None, which means there is no limit.

EMAIL_MAX_RETRIES

The maximum number of times an email can be deferred before being marked as failed. The default is None, which means there is no limit.

EMPTY_QUEUE_SLEEP

The time in seconds to wait before checking the queue for new emails to send. The default is 30 seconds.

EMAIL_THROTTLE

The time in seconds to sleep between sending emails, to avoid potential rate limits or overloading your SMTP server. The default is 0 seconds.

MESSAGES_BATCH_SIZE

The batch size to use when bulk creating Messages in the database. The default is None, which means Django's default batch size will be used.

Inspiration

This package is heavily inspired by the django-mailer package. django-mailer is licensed under the MIT license, which is also the license used for this package. The required copyright notice is included in the LICENSE file for this package.