server_ses_email_forwarder.py

import boto3
import email
from email.mime.text import MIMEText
from email.mime.multipart import MIMEMultipart
from botocore.exceptions import ClientError
import logging
from email.utils import parseaddr, formataddr
import hashlib

# Configure logging.
logger = logging.getLogger()
logger.setLevel(logging.INFO)

# Set vars.
REGION = 'us-west-2'
S3_BUCKET = 'forwarder.charleschristensen.co'
S3_PREFIX = None
EMAIL_DEFAULT = '[email protected]'
EMAIL_MAPPINGS = {
    '[email protected]': '[email protected]',
    '[email protected]': '[email protected]',
    '[email protected]': '[email protected]',
    '[email protected]': '[email protected]',
    '[email protected]': '[email protected]',
    '[email protected]': '[email protected]',
    '[email protected]': '[email protected]'
    # REMEMBER THAT RECIPIENT EMAILS IN HERE MUST BE VERIFIED IN SES!!!
}

def get_message_from_s3(message_id):
    if S3_PREFIX:
        object_path = f"{S3_PREFIX}/{message_id}"
    else:
        object_path = message_id

    client_s3 = boto3.client("s3")
    object_s3 = client_s3.get_object(
        Bucket=S3_BUCKET,
        Key=object_path
    )
    file = object_s3['Body'].read()

    return file

def send_raw_email(raw_message, source, destination):
    
    mailobject = email.message_from_bytes(raw_message)
    new_message = MIMEMultipart('alternative')

    # Parse original from header to extract display name and email.
    original_from = mailobject.get('From')
    display_name, email_addr = parseaddr(original_from)
    email_hash = hashlib.md5(email_addr.lower().encode('utf-8')).hexdigest()[:16].upper()
    email_sender = email_hash + "@forwarder.charleschristensen.co"
    
    # Create new from header with original display name and verified sender email.
    new_from = formataddr((display_name, email_sender)) if display_name else email_sender

    # Copy essential headers.
    for header in ['To', 'Subject', 'Date', 'Message-ID']:
        if mailobject.get(header):
            new_message[header] = mailobject.get(header)
    new_message.add_header('From', new_from)
    new_message.add_header('Reply-To', source)

    # Extract and attach preferred parts. Prioritize HTML, include plain text only if no HTML.
    has_html = False
    html_payload = None
    html_subtype = None
    text_payload = None
    text_subtype = None

    if mailobject.is_multipart():
        for part in mailobject.get_payload():
            content_type = part.get_content_type()
            if content_type == 'text/html':
                has_html = True
                html_payload = part.get_payload(decode=True)
                html_subtype = part.get_content_subtype()  # Should be 'html'
            elif content_type == 'text/plain':
                text_payload = part.get_payload(decode=True)
                text_subtype = part.get_content_subtype()  # Should be 'plain'
    else:
        content_type = mailobject.get_content_type()
        if content_type == 'text/html':
            has_html = True
            html_payload = mailobject.get_payload(decode=True)
            html_subtype = mailobject.get_content_subtype()
        elif content_type == 'text/plain':
            text_payload = mailobject.get_payload(decode=True)
            text_subtype = mailobject.get_content_subtype()

    # Attach HTML, if present.
    if has_html and html_payload is not None:
        # Decode payload and re-wrap in MIMEText to ensure proper handling
        html_text = html_payload.decode('utf-8', errors='replace')
        new_message.attach(MIMEText(html_text, html_subtype, 'utf-8'))
    
    # Attach plain text, only if no HTML.
    if not has_html and text_payload is not None:
        text_text = text_payload.decode('utf-8', errors='replace')
        new_message.attach(MIMEText(text_text, text_subtype, 'utf-8'))

    # Special case. Fallback to attaching both.
    if new_message.get_payload() == []:
        if mailobject.is_multipart():
            for part in mailobject.get_payload():
                new_message.attach(part)
        else:
            new_message.attach(MIMEText(mailobject.get_payload(decode=True).decode('utf-8', errors='replace'), mailobject.get_content_subtype(), 'utf-8'))

    modified_message = new_message.as_bytes()

    client_ses = boto3.client('ses', REGION)
    try:
        response = client_ses.send_raw_email(
            Source=email_sender,
            Destinations=[destination],
            RawMessage={
                'Data': modified_message
            }
        )
        return f"Email Sent! Message ID: {response['MessageId']}"
    except ClientError as e:
        return f"Error! {e.response['Error']['Message']}"

def lambda_handler(event, context):
    # Get message details from SES event
    message_id = event['Records'][0]['ses']['mail']['messageId']
    to_address = event['Records'][0]['ses']['mail']['destination'][0]
    
    # Log initial receipt
    logger.info(f"Received Message ID: {message_id} for {to_address}")
    
    # Retrieve the raw email from S3
    raw_email = get_message_from_s3(message_id)
    
    # Parse the original email to get the source
    mailobject = email.message_from_bytes(raw_email)
    original_from = mailobject.get('From')
    
    # Log the full message
    logger.info(f"From: {original_from}")
    logger.info(f"Raw Message: {raw_email.decode('utf-8')}")
    
    # Check if the recipient exists in our mappings
    if to_address in EMAIL_MAPPINGS:
        forward_to = EMAIL_MAPPINGS[to_address.lower()]
    else:
        forward_to = EMAIL_DEFAULT
    
    # Forward the modified email
    result = send_raw_email(raw_email, original_from, forward_to)
    logger.info(result)
    
    return {
        'statusCode': 200,
        'body': result
    }