SMTP Firewall

SMTP Firewall serves as a sidecar container alongside your primary application. It filters emails before they reach your email service provider.

Key features:

• Rate Limit with a mail queue
• Dropping emails if the app sends too frequently to a single recipient
• Bad Domain Filter
• Support SMTP and multiple email service providers

Getting started

Using a Docker Compose file

Instead of running SMTP Firewall as a sidecar in a Kubernetes Pod, you may make use of Docker Compose to try running it.

version: '3'

services:
  smtp:
    image: rnwood/smtp4dev
    ports:
      - 3000:80
  smtp_firewall:
    image: relatedbits/smtp-firewall
    environment:
      FILTER_BAD_DOMAIN_ENABLED: true
  app:
    image: YOUR_APPLICATION_IMAGE # Replace with your app image
    environment:
      SMTP_HOST: smtp_firewall # Set SMTP Host
      SMTP_PORT: 1025          # Set SMTP Port

Launch the containers using:

docker compose up -d

Open your application and send an email.

You may then open http://localhost:3000 to see if the email is being dropped.

Prepare an email blacklist

SMTP Firewall reads from bad_domains.txt for the email blacklist. Each line in the file represents a domain name.

You may start from downloading email blacklist online:

• https://github.com/disposable-email-domains/disposable-email-domains

Select an email service proviers

SMTP

Environment variables:

Variable	Value(example)
SENDER_TYPE	smtp
SENDER_SMTP_ADDR	smtp:25

AWS SES

Environment variables:

Variable	Value(example)
SENDER_TYPE	awsses
SENDER_AWSSES_TIMEOUT	5

Mailjet

Environment variables:

Variable	Value(example)
SENDER_TYPE	mailjet
SENDER_MAILJET_BASEURL	(Leave it blank to apply the default base URL defined by official library)
SENDER_MAILJET_APIKEY_PUBLIC	APIKEY_PUBLIC
SENDER_MAILJET_APIKEY_PRIVATE	APIKEY_PRIVATE

Configuration

Environment variables

Variable	Default Value
SMTP_SERVER_ADDR	0.0.0.0:1025
SMTP_SERVER_ALLOW_INSECURE_AUTH	true
FILTER_BAD_DOMAIN_ENABLED	false
RATELIMIT	10
QUEUE_CAPACITY	100
TIMEDMAP_COOLDOWN_SECONDS_FOR_SINGLE_RECIPIENT	30
TIMEDMAP_CLEANUP_PER_N_SECOND	60