SMTP2HTTP (email-to-web)

smtp2http is a simple smtp server that resends the incoming email to the configured web endpoint (webhook) as a basic http post request.

Features

• Convert SMTP emails to HTTP webhook calls
• Postmark webhook format support - Compatible with Postmark's webhook JSON structure
• Environment variable configuration - Configure via .env file or environment variables
• SPF validation and domain filtering
• Attachment and embedded file support (base64 encoded)
• Docker support for easy deployment

Dev

• go mod vendor
• go build

Dev with Docker

Locally :

• go mod vendor
• docker build -f Dockerfile.dev -t smtp2http-dev .
• docker run -p 25:25 smtp2http-dev --timeout.read=50 --timeout.write=50 --webhook=http://some.hook/api

Or build it as it comes from the repo :

• docker build -t smtp2http .
• docker run -p 25:25 smtp2http --timeout.read=50 --timeout.write=50 --webhook=http://some.hook/api

The timeout options are of course optional but make it easier to test in local with telnet localhost 25

Testing

Test the SMTP server using telnet:

telnet localhost 25
HELO zeus
MAIL FROM:<email@from.com>
RCPT TO:<youremail@example.com>
DATA
your mail content
.

Docker (production)

Docker images arn't available online for now See "Dev with Docker" above

• docker run -p 25:25 smtp2http --webhook=http://some.hook/api

Configuration

Command Line Usage

# Basic usage
smtp2http --listen=:25 --webhook=http://localhost:8080/api/smtp-hook

# Postmark format with authentication
smtp2http --postmark --postmark-token=your-server-token

# View all options
smtp2http --help

Environment Variables

Copy .env.example to .env and configure:

# SMTP Server Settings
SMTP_LISTEN_ADDR=:25
WEBHOOK_URL=https://your-webhook.com/api

# Postmark Integration
USE_POSTMARK_FORMAT=true
POSTMARK_SERVER_TOKEN=your-server-token

# Optional settings
ALLOWED_DOMAIN=yourdomain.com
SMTP_USER=username
SMTP_PASS=password

Postmark Integration

When using --postmark flag:

• Email data is converted to Postmark's webhook JSON format
• Webhook URL defaults to https://api.postmarkapp.com/email
• Include --postmark-token to send the X-Postmark-Server-Token header
• All Postmark-specific fields are properly mapped (FromFull, ToFull, etc.)

# Simple Postmark setup (uses Postmark API endpoint)
smtp2http --postmark --postmark-token=your-server-token

# Custom webhook with Postmark format
smtp2http --postmark --postmark-token=your-token --webhook=https://your-app.com/webhook

Contribution

Original repo from @alash3al Thanks to @aranajuan