A simple Python email gateway

2017-05-10T13:23:11+00:00

Say you have a Django web application that you want to integrate with emails to make it possibile to send data and files to your web application over SMTP.

The good news is that Python has a simple SMTP daemon in the standard library, together with modules to parse emails. Let’s see how to create a simple email gateway on top of these tools.

Using the following Python module you can setup a simple pure Python email server on port 25, parse the incoming emails and make a multipart/form-data POST HTTP request to your web application. You’ll need the awesome Requests library for the HTTP request to work.

import smtpd import asyncore import logging import email from email.header import decode_header import requests logger = logging.getLogger(__name__) class CustomSMTPServer(smtpd.SMTPServer): def process_message(self, peer, mailfrom, rcpttos, data): try: logger.debug('Receiving message from: %s:%d' % peer) logger.debug('Message addressed from: %s' % mailfrom) logger.debug('Message addressed to: %s' % str(rcpttos)) msg = email.message_from_string(data) subject = '' for encoded_string, charset in decode_header(msg.get('Subject')): try: if charset is not None: subject += encoded_string.decode(charset) else: subject += encoded_string except: logger.exception('Error reading part of subject: %s charset %s' % (encoded_string, charset)) logger.debug('Subject: %s' % subject) text_parts = [] attachments = {} logger.debug('Headers: %s' % msg.items()) # YOU CAN DO SOME SECURITY CONTROLS HERE if (not mailfrom.endswith("@example.com") or not msg.get('Mail-Header') == 'expected value'): raise Exception("Email not trusted") # loop on the email parts for part in msg.walk(): if part.get_content_maintype() == 'multipart': continue c_type = part.get_content_type() c_disp = part.get('Content-Disposition') # text parts will be appended to text_parts if c_type == 'text/plain' and c_disp == None: text_parts.append(part.get_payload(decode=True).strip()) # ignore html part elif c_type == 'text/html': continue # attachments will be sent as files in the POST request else: filename = part.get_filename() filecontent = part.get_payload(decode=True) if filecontent is not None: if filename is None: filename = 'untitled' attachments['file%d' % len(attachments)] = (filename, filecontent) body = '\n'.join(text_parts) except: logger.exception('Error reading incoming email') else: # this data will be sent as POST data data = { 'subject': subject, 'body': body, 'from': mailfrom, } url = 'http://yourserver.example.com/email-receive/' logger.debug('Sending data and files to %s' % url) try: r = requests.post(url, data=data, files=attachments) r.raise_for_status() except: logger.exception('Error in server request') logger.debug(data) logger.debug(attachments) else: logger.debug('Response from server: %s %s' % (r.status_code, r.text)) return if __name__ == '__main__': ch = logging.StreamHandler() ch.setLevel(logging.DEBUG) formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s') ch.setFormatter(formatter) logger.setLevel(logging.DEBUG) logger.addHandler(ch) server = CustomSMTPServer(('111.111.111.111', 25), None) # use your public IP here asyncore.loop()

In a production environment you can setup supervisor to launch your simple SMTP server. With a simple configuration like this:

[program:smtp_server]
command = /home/ubuntu/.virtualenvs/venv/bin/python /home/ubuntu/mail_gateway/smtp_server.py
user = root

Then try to send an email to your server, if the server public IP has been associated to a DNS record yourserver.example.com you can use something like test@yourserver.example.com as a recipient, and you should see the incoming email in the logs.

Have fun with emails!

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A simple Python email gateway