app.py

import logging
import ssl
from aiosmtpd.controller import Controller
from aiosmtpd.handlers import Sink
from aiosmtpd.smtp import SMTP, AuthResult, LoginPassword
from email.policy import default
from typing import Optional

# Configure logging
logging.basicConfig(level=logging.INFO)
logger = logging.getLogger("smtp_server")

# SMTP Server Configuration
SMTP_HOST = "0.0.0.0"  # Bind to all interfaces
SMTP_PORT = 587         # Standard SMTP submission port
TLS_CERTFILE = "cert.pem"  # Path to your SSL certificate
TLS_KEYFILE = "key.pem"    # Path to your SSL private key

# Authentication Credentials (for demo purposes; use a secure vault in production)
VALID_USERS = {
    "user1": "password1",
    "user2": "password2",
}

class AuthenticatedSMTPHandler(Sink):
    async def handle_AUTH(self, server: SMTP, args: str, mechanism: str) -> Optional[AuthResult]:
        if mechanism.upper() != "LOGIN":
            return AuthResult(success=False, handled=False)
        return None

    async def handle_AUTH_LOGIN(self, server: SMTP, args: str) -> Optional[AuthResult]:
        try:
            username, password = args.split()
            if username in VALID_USERS and VALID_USERS[username] == password:
                return AuthResult(success=True, auth_data=LoginPassword(username, password))
            else:
                return AuthResult(success=False, message="Invalid credentials")
        except Exception as e:
            logger.error(f"Authentication error: {e}")
            return AuthResult(success=False, message="Authentication failed")

    async def handle_DATA(self, server: SMTP, session, envelope):
        # Log the received email
        logger.info(f"Received email from: {envelope.mail_from}")
        logger.info(f"Recipients: {envelope.rcpt_tos}")
        logger.info(f"Message data:\n{envelope.content.decode('utf-8')}")
        return "250 Message accepted for delivery"

def start_smtp_server():
    # Create SSL context for TLS
    ssl_context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
    ssl_context.load_cert_chain(TLS_CERTFILE, TLS_KEYFILE)

    # Create the SMTP handler
    handler = AuthenticatedSMTPHandler()

    # Start the SMTP server with TLS and authentication
    controller = Controller(
        handler,
        hostname=SMTP_HOST,
        port=SMTP_PORT,
        enable_SMTPUTF8=True,
        ssl_context=ssl_context,
        auth_required=True,
    )

    logger.info(f"Starting SMTP server on {SMTP_HOST}:{SMTP_PORT} with TLS and authentication...")
    controller.start()
    try:
        # Keep the server running
        while True:
            pass
    except KeyboardInterrupt:
        logger.info("Shutting down SMTP server...")
        controller.stop()

if __name__ == "__main__":
    start_smtp_server()