Eternals Mailer

Stable

Eternals Mailer is an email testing tool for developers. It captures emails sent by your application during development so you can inspect them in a clean web UI. Built with Go for SMTP capture, NestJS for the API, React for the web UI, PostgreSQL for persistence, and Redis for caching. Point your app’s SMTP config at Eternals Mailer, and every outgoing email lands in your local inbox — safely, instantly.

Tech Stack

Layer	Technology
Web UI	React
API server	NestJS
SMTP / core	Go
Database	PostgreSQL
Cache	Redis

Features

• Token-based authentication — Secure API access with JWT tokens
• Real-time email capture — Instant capture of all outgoing emails via SMTP
• Full message inspection — View HTML/text bodies, headers, and attachments
• Modern web UI — Clean React interface with dark mode support

Use Cases

• Test email templates — Preview and validate email layouts before production
• Debug email delivery — Inspect headers, content, and attachments during development
• Verify SMTP integration — Confirm your app’s email functionality without sending real emails
• QA workflows — Review automated emails in a safe, isolated environment

Architecture Overview

Your Application → SMTP (port 1025) → Go SMTP server → NestJS API → PostgreSQL
                                                              ↓              ↓
                                                      React Web UI      Redis
                                                      (port 8502)

Tip

Configure your application to send emails to localhost:1025, then open http://localhost:8502 to view captured emails.

Quick Start

Docker

docker run -d \
  --name ec-mailer \
  --restart always \
  -p 8502:8502 \
  -p 1025:1025 \
  -e POSTGRES_URL=postgresql://postgres:password@host:5432/mailer \
  -v mailer:/app/attachments \
  eternalscloud/mailer:latest

Once the container is running:

• Web UI: Open http://localhost:8502 in your browser
• SMTP Server: Configure your application to send mail to localhost:1025

Docker Compose

services:
  ec-mailer:
    image: eternalscloud/mailer:latest
    container_name: ec-mailer
    restart: always
    ports:
      - "8502:8502"
      - "1025:1025"
    environment:
      - POSTGRES_URL=postgresql://postgres:password@db:5432/mailer
    volumes:
      - mailer:/app/attachments
    depends_on:
      - db

  db:
    image: postgres:18.4
    restart: always
    environment:
      POSTGRES_PASSWORD: password
      POSTGRES_DB: mailer
    volumes:
      - postgres:/var/lib/postgresql/data

volumes:
  mailer:
  postgres:

Run with:

docker compose up -d

Connecting Your Application

Configure your application’s SMTP settings to point to Eternals Mailer:

Setting	Value
Host	localhost (or container name in Docker networks)
Port	1025

Node.js

const transporter = nodemailer.createTransport({
  host: 'localhost',
  port: 1025,
  secure: false
});

Python

import smtplib

with smtplib.SMTP('localhost', 1025) as server:
    server.sendmail(sender, recipient, message)

Go

err := smtp.SendMail(
    "localhost:1025",
    nil,
    sender,
    []string{recipient},
    []byte(message),
)

Configuration

Environment Variables

Variable	Required	Description
POSTGRES_URL	Yes	PostgreSQL connection URL (e.g., postgresql://postgres:password@host:5432/mailer)

Exposed Ports

Port	Description
8502	Web UI and REST API
1025	SMTP server

Volumes

Path	Description
/app/attachments	Mail attachment storage

Caution

Mount a volume to /app/attachments to persist email attachments across container restarts.

Vision

Eternals Mailer provides developers with a safe, self-hosted environment for testing email functionality. Catch every email, inspect it instantly, and ship with confidence — no emails ever leave your development environment.