Mailjet Postfix Transport

mailjet-relay.py

#!/usr/bin/env python3
"""
Mailjet Email Relay Script
==========================

Background, I had some issues working with mailjet's smtp relay.  However, I found
their API to be reliable. So here's my custom python script acts as a 
Postfix transport to relay emails via Mailjet API.

Setup Instructions:
1. Install required Python package: pip3 install requests
2. Set your Mailjet API credentials as environment variables:
   export MAILJET_API_KEY="your_api_key_here"
   export MAILJET_API_SECRET="your_api_secret_here"
3. Set default sender domain (optional):
   export MAILJET_DEFAULT_DOMAIN="yourdomain.com"
4. Make script executable: chmod +x mailjet-relay.py

Postfix Integration:
1. Add to /etc/postfix/master.cf:
   mailjet-api unix -       n       n       -       -       pipe
     flags=FR user=postfix argv=/path/to/mailjet-relay.py ${recipient}

2. Add to transport maps (e.g., /etc/postfix/transport):
   @yourdomain.com mailjet-api:

3. Update Postfix config:
   postmap /etc/postfix/transport
   postfix reload

Usage:
- Script reads email from stdin and recipient from command line argument
- Supports plain text, HTML, and attachments
- Uses Mailjet API v3.1 for sending

Environment Variables:
- MAILJET_API_KEY: Your Mailjet API key (required)
- MAILJET_API_SECRET: Your Mailjet API secret (required)
- MAILJET_DEFAULT_DOMAIN: Default domain for fallback sender (default: localhost)
- MAILJET_DEFAULT_USER: Default username for fallback sender (default: postmaster)

By: Rick L Bird
License: MIT
"""

import sys
import json
import base64
import requests
import os
from email import message_from_string
from email.utils import parseaddr

# Mailjet API configuration
API_KEY = os.environ.get('MAILJET_API_KEY')
API_SECRET = os.environ.get('MAILJET_API_SECRET')
API_URL = "https://api.mailjet.com/v3.1/send"

# Default sender configuration
DEFAULT_DOMAIN = os.environ.get('MAILJET_DEFAULT_DOMAIN', 'localhost')
DEFAULT_USER = os.environ.get('MAILJET_DEFAULT_USER', 'postmaster')
DEFAULT_SENDER = f"{DEFAULT_USER}@{DEFAULT_DOMAIN}"

def send_via_mailjet():
    # Check for required credentials
    if not API_KEY or not API_SECRET:
        print("Error: MAILJET_API_KEY and MAILJET_API_SECRET environment variables must be set", file=sys.stderr)
        sys.exit(74)  # Configuration error
    
    # Get recipient from command line argument
    recipient_email = sys.argv[1] if len(sys.argv) > 1 else None
    
    # Read the email from stdin
    raw_email = sys.stdin.buffer.read()
    
    # Parse the email
    from email.parser import BytesParser
    from email.policy import default
    msg = BytesParser(policy=default).parsebytes(raw_email)
    
    # Extract headers
    from_addr = parseaddr(msg.get('From', DEFAULT_SENDER))
    to_header = msg.get('To', '')
    cc_header = msg.get('Cc', '')
    bcc_header = msg.get('Bcc', '')
    subject = msg.get('Subject', 'No Subject')
    
    # Use command line recipient if no To header
    to_addrs = []
    if recipient_email:
        to_addrs = [('', recipient_email)]
    elif to_header:
        to_addrs = [parseaddr(addr.strip()) for addr in to_header.split(',') if addr.strip()]
    
    cc_addrs = []
    if cc_header:
        cc_addrs = [parseaddr(addr.strip()) for addr in cc_header.split(',') if addr.strip()]
    
    bcc_addrs = []
    if bcc_header:
        bcc_addrs = [parseaddr(addr.strip()) for addr in bcc_header.split(',') if addr.strip()]
    
    
    # Get message body and attachments
    body = ""
    html_body = ""
    attachments = []
    
    if msg.is_multipart():
        for part in msg.walk():
            content_type = part.get_content_type()
            content_disposition = str(part.get('Content-Disposition', ''))
            
            if content_type == "text/plain" and 'attachment' not in content_disposition:
                body = part.get_payload(decode=True).decode('utf-8', errors='ignore')
            elif content_type == "text/html" and 'attachment' not in content_disposition:
                html_body = part.get_payload(decode=True).decode('utf-8', errors='ignore')
                # Remove any escaping that might cause issues with DOCTYPE
                html_body = html_body.replace('<\\!', '<!')
            elif 'attachment' in content_disposition or part.get_filename():
                # Handle attachment
                filename = part.get_filename()
                if filename:
                    attachment_data = part.get_payload(decode=True)
                    if attachment_data:
                        attachments.append({
                            "ContentType": content_type,
                            "Filename": filename,
                            "Base64Content": base64.b64encode(attachment_data).decode('utf-8')
                        })
    else:
        body = msg.get_payload(decode=True).decode('utf-8', errors='ignore')
    
    
    # If no HTML body, use plain text
    if not html_body:
        html_body = f"<pre>{body}</pre>"
    
    # Build Mailjet API payload
    message_data = {
        "From": {
            "Email": from_addr[1] if from_addr[1] else DEFAULT_SENDER,
            "Name": from_addr[0] if from_addr[0] else "Mail System"
        },
        "To": [
            {
                "Email": to_addr[1],
                "Name": to_addr[0] if to_addr[0] else to_addr[1]
            } for to_addr in to_addrs if to_addr[1]
        ],
        "Subject": subject,
        "TextPart": body,
        "HTMLPart": html_body
    }
    
    # Add CC if any
    if cc_addrs:
        message_data["Cc"] = [
            {
                "Email": cc_addr[1],
                "Name": cc_addr[0] if cc_addr[0] else cc_addr[1]
            } for cc_addr in cc_addrs if cc_addr[1]
        ]
    
    # Add BCC if any
    if bcc_addrs:
        message_data["Bcc"] = [
            {
                "Email": bcc_addr[1],
                "Name": bcc_addr[0] if bcc_addr[0] else bcc_addr[1]
            } for bcc_addr in bcc_addrs if bcc_addr[1]
        ]
    
    # Add attachments if any
    if attachments:
        message_data["Attachments"] = attachments
    
    data = {"Messages": [message_data]}
    
    
    # Send via Mailjet API
    try:
        response = requests.post(
            API_URL,
            auth=(API_KEY, API_SECRET),
            headers={'Content-Type': 'application/json'},
            json=data
        )
        
        
        if response.status_code == 200:
            result = response.json()
            if result.get('Messages', [{}])[0].get('Status') == 'success':
                sys.exit(0)  # Success
            else:
                print(f"Mailjet API error: {result}", file=sys.stderr)
                sys.exit(75)  # Temporary failure
        else:
            print(f"HTTP {response.status_code}: {response.text}", file=sys.stderr)
            sys.exit(75)  # Temporary failure
            
    except Exception as e:
        print(f"Error sending via Mailjet API: {e}", file=sys.stderr)
        sys.exit(75)  # Temporary failure

if __name__ == "__main__":
    send_via_mailjet()