SMTPServer

A lightweight Python SMTP server for receiving and parsing emails, with customizable callbacks for further processing. Useful for development, testing, or building custom mail processing pipelines.

• Minimal SMTP server implementation using raw sockets
• Supports core SMTP commands: HELO, MAIL FROM, RCPT TO, DATA, QUIT
• Parses raw email headers and multipart content (plain text & HTML)
• Built-in callback mechanism for custom email handling
• Logs all server activity for debugging and observability

SMTPServer/
├── smtp_server.py      # Core SMTP server logic
├── email_parser.py     # Email header and body parser
└── example.py          # Example usage with console callback

git clone https://github.com/your-username/SMTPServer.git
cd SMTPServer

python example.py

The server will start on port 25 and listen for incoming SMTP connections. On receiving an email, it will parse it and print the details to the console.

• smtp_server.py: Sets up a socket-based SMTP server. On receiving complete email data, it uses EmailParser to decode and structure the content.
• email_parser.py: Extracts common headers (From, To, Subject, etc.) and separates multipart content into plain text and HTML.
• example.py: Demonstrates how to instantiate the server and print parsed email details using a callback.

You can customize the server in example.py:

server = SMTPServer(
    host='0.0.0.0',     # Change to '127.0.0.1' if you only want localhost access
    port=25,            # Make sure port 25 is available or use a different one
    email_callback=email_callback  # Your handler for incoming parsed emails
)

• Standard Python 3 libraries only (no external packages required)

Starting SMTP server...
Received new email:
From: Jane <jane@example.com>
To: John <john@example.com>
Subject: Hello!
Date: Sun, 13 Jul 2025 10:15:00 +0000
Message ID: abc123@example.com

Content:
Plain text version:
This is a test email sent to your SMTP server.

MIT License. See LICENSE for more details.

Developed by Bastian Carou.