Mandrill-compatible SMTP Redirector (Go)

Overview

• Implements a subset of Mandrill Transactional API endpoints for local development.
• Accepts Mandrill-style JSON requests and relays messages to a regular SMTP server.
• Stores messages in-memory for search, info, and content endpoints.
• Supports simple scheduling of messages.

Endpoints

• POST /messages/send and /messages/send.json
• POST /api/1.0/messages/send.json (alias for SDK compatibility)
• POST /messages/send-template and /messages/send-template.json
• POST /api/1.0/messages/send-template.json
• POST /messages/send-raw and /messages/send-raw.json
• POST /api/1.0/messages/send-raw.json
• POST /messages/parse and /messages/parse.json
• POST /api/1.0/messages/parse.json
• POST /messages/info and /messages/info.json
• POST /api/1.0/messages/info.json
• POST /messages/content and /messages/content.json
• POST /api/1.0/messages/content.json
• POST /messages/search and /messages/search.json
• POST /api/1.0/messages/search.json
• POST /messages/search-time-series and /messages/search-time-series.json
• POST /api/1.0/messages/search-time-series.json
• POST /messages/list-scheduled and /messages/list-scheduled.json
• POST /api/1.0/messages/list-scheduled.json
• POST /messages/cancel-scheduled and /messages/cancel-scheduled.json
• POST /api/1.0/messages/cancel-scheduled.json
• POST /messages/reschedule and /messages/reschedule.json
• POST /api/1.0/messages/reschedule.json
• GET /healthz

Configuration (env)

• SMTP_HOST (default: localhost)
• SMTP_PORT (default: 1025)
• SMTP_USERNAME (optional)
• SMTP_PASSWORD (optional)
• SMTP_TLS one of none (default), starttls, tls
• SMTP_INSECURE_TLS true|false (default: false)
• MANDRILL_KEYS comma-separated list. If set, incoming key must match one of these.
• DEFAULT_FROM_NAME default sender name when missing (default: Mandrill Dev).
• PORT HTTP port (default: 8080).

Run locally

1. Run an SMTP server (e.g., MailHog): docker run -p 1025:1025 -p 8025:8025 mailhog/mailhog
2. Start server:

SMTP_HOST=localhost SMTP_PORT=1025 PORT=8080 go run ./cmd/mandrill-dev

Docker

docker build -t mandrill-dev .
docker run --rm -p 8080:8080 \
  -e SMTP_HOST=host.docker.internal \
  -e SMTP_PORT=1025 \
  mandrill-dev

Docker Compose (with smtp4dev)

This repo includes a docker-compose.yml that brings up smtp4dev and this Mandrill-compatible server together.

docker compose -f compose.yml up --build

• Mandrill API: http://localhost:8080
• smtp4dev UI: http://localhost:3000

The Mandrill server relays email to the smtp4dev container (SMTP_HOST=smtp4dev, SMTP_PORT=25).

Additional example services:

• bun-http-client posts to /api/1.0/messages/send.json.
• bun-sdk-client uses the SDK example configured to talk to the local server via MC_BASE.
• bun-send-template-client exercises /api/1.0/messages/send-template.json with merge vars.

Health checks

• The server exposes GET /healthz which returns 200 OK and ok body.
• The Docker image includes a HEALTHCHECK that runs /mandrill-dev -healthcheck against http://127.0.0.1:$PORT/healthz.

Client example

• Go client: examples/go-client/main.go (Compose service: client).
• Node client (HTTP): examples/node-client/http-client.js (Compose service: node-http-client).
• Node client (Official SDK): examples/node-client/sdk-client.js — by default the SDK targets mandrillapp.com. When MC_BASE is set (e.g. http://localhost:8080/api/1.0), this example will post directly to the local dev server instead of the public API.
• Node client (send-template): examples/node-client/send-template.js — uses the official SDK by default. If MC_BASE is set (e.g., http://localhost:8080/api/1.0), it posts directly to the local dev server’s /messages/send-template.json.

Run the client with Compose:

docker compose -f compose.yml up --build client

Or run locally against a running server:

API_BASE=http://localhost:8080 \
KEY=dev \
FROM=sender@example.com \
TO=user@example.com \
go run ./examples/go-client

Node HTTP client (no SDK):

API_BASE=http://localhost:8080 \
KEY=dev \
FROM=sender@example.com \
TO=user@example.com \
node examples/node-client/http-client.js

Node SDK client (requires package install):

cd examples/node-client
npm install
# Point to local server via MC_BASE
MC_BASE=http://localhost:8080/api/1.0 \
KEY=dev \
FROM=sender@example.com \
TO=user@example.com \
node sdk-client.js

Examples

• Send:

curl -s localhost:8080/messages/send -H 'Content-Type: application/json' -d '{
  "key":"dev",
  "message":{
    "from_email":"sender@example.com",
    "from_name":"Sender",
    "subject":"Hello",
    "text":"Plain text body",
    "html":"<b>HTML body</b>",
    "to":[{"email":"user@example.com","type":"to"}],
    "headers":{"Reply-To":"reply@example.com"}
  }
}' | jq .

• Send raw:

curl -s localhost:8080/messages/send-raw -H 'Content-Type: application/json' -d '{
  "key":"dev",
  "from_email":"sender@example.com",
  "to":["user@example.com"],
  "raw_message":"From: Sender <sender@example.com>\r\nTo: user@example.com\r\nSubject: Raw test\r\n\r\nRaw body\r\n"
}' | jq .

Notes

• This is for local development; there is no persistence across restarts.
• Attachments and inline images are supported via base64 in attachments and images arrays.
• Template sending performs simple *|NAME|* token replacement using template_content items.
• Scheduler is a best-effort background loop checking once per second. Node send-template client (local server):

MC_BASE=http://localhost:8080/api/1.0 \
KEY=dev \
FROM=sender@example.com \
TO=user@example.com \
node examples/node-client/send-template.js