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app-MAIL-temp/email_handler.py

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Python
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"""
Handle the email *forward* and *reply*. phase. There are 3 actors:
- website: who sends emails to alias@sl.co address
- SL email handler (this script)
- user personal email: to be protected. Should never leak to website.
This script makes sure that in the forward phase, the email that is forwarded to user personal email has the following
envelope and header fields:
Envelope:
mail from: @website
rcpt to: @personal_email
Header:
From: @website
To: alias@sl.co # so user knows this email is sent to alias
Reply-to: special@sl.co # magic HERE
And in the reply phase:
Envelope:
mail from: @website
rcpt to: @website
Header:
From: alias@sl.co # so for website the email comes from alias. magic HERE
To: @website
The special@sl.co allows to hide user personal email when user clicks "Reply" to the forwarded email.
It should contain the following info:
- alias
- @website
"""
import time
from email.message import EmailMessage
from email.parser import Parser
from email.policy import SMTPUTF8
from smtplib import SMTP
from aiosmtpd.controller import Controller
from app.config import EMAIL_DOMAIN, POSTFIX_SERVER, URL
from app.email_utils import notify_admin
from app.extensions import db
from app.log import LOG
from app.models import GenEmail, ForwardEmail, ForwardEmailLog
from app.utils import random_words
from server import create_app
# fix the database connection leak issue
# use this method instead of create_app
def new_app():
app = create_app()
@app.teardown_appcontext
def shutdown_session(response_or_exc):
# same as shutdown_session() in flask-sqlalchemy but this is not enough
db.session.remove()
# dispose the engine too
db.engine.dispose()
return app
class MailHandler:
async def handle_DATA(self, server, session, envelope):
LOG.debug(">>> New message <<<")
LOG.debug("Mail from %s", envelope.mail_from)
LOG.debug("Rcpt to %s", envelope.rcpt_tos)
message_data = envelope.content.decode("utf8", errors="replace")
# Only when debug
# LOG.debug("Message data:\n")
# LOG.debug(message_data)
# host IP, setup via Docker network
smtp = SMTP(POSTFIX_SERVER, 25)
msg = Parser(policy=SMTPUTF8).parsestr(message_data)
if not envelope.rcpt_tos[0].startswith("reply+"): # Forward case
LOG.debug("Forward phase")
app = new_app()
with app.app_context():
return self.handle_forward(envelope, smtp, msg)
else:
LOG.debug("Reply phase")
app = new_app()
with app.app_context():
return self.handle_reply(envelope, smtp, msg)
def handle_forward(self, envelope, smtp, msg: EmailMessage) -> str:
"""return *status_code message*"""
alias = envelope.rcpt_tos[0] # alias@SL
gen_email = GenEmail.get_by(email=alias)
if not gen_email:
LOG.d("alias %s not exist")
return "510 Email not exist"
user_email = gen_email.user.email
website_email = get_email_part(msg["From"])
forward_email = ForwardEmail.get_by(
gen_email_id=gen_email.id, website_email=website_email
)
if not forward_email:
LOG.debug(
"create forward email for alias %s and website email %s",
alias,
website_email,
)
# todo: make sure reply_email is unique
reply_email = f"reply+{random_words()}@{EMAIL_DOMAIN}"
forward_email = ForwardEmail.create(
gen_email_id=gen_email.id,
website_email=website_email,
website_from=msg["From"],
reply_email=reply_email,
)
db.session.commit()
forward_log = ForwardEmailLog.create(forward_id=forward_email.id)
if gen_email.enabled:
# add custom header
add_or_replace_header(msg, "X-SimpleLogin-Type", "Forward")
# remove reply-to header if present
if msg["Reply-To"]:
LOG.d("Delete reply-to header %s", msg["Reply-To"])
del msg["Reply-To"]
# change the from header so the sender comes from @SL
# so it can pass DMARC check
# replace the email part in from: header
from_header = (
get_email_name(msg["From"])
+ " - "
+ website_email.replace("@", " at ")
+ f" <{forward_email.reply_email}>"
)
msg.replace_header("From", from_header)
LOG.d("new from header:%s", from_header)
# add List-Unsubscribe header
unsubscribe_link = f"{URL}/dashboard/unsubscribe/{gen_email.id}"
add_or_replace_header(msg, "List-Unsubscribe", f"<{unsubscribe_link}>")
add_or_replace_header(
msg, "List-Unsubscribe-Post", "List-Unsubscribe=One-Click"
)
# remove DKIM-Signature as Postfix will add this header
if msg["DKIM-Signature"]:
LOG.d("Remove DKIM-Signature %s", msg["DKIM-Signature"])
del msg["DKIM-Signature"]
original_subject = msg["Subject"]
LOG.d(
"Forward mail from %s to %s, subject %s, mail_options %s, rcpt_options %s ",
website_email,
user_email,
original_subject,
envelope.mail_options,
envelope.rcpt_options,
)
# smtp.send_message has UnicodeEncodeErroremail issue
# encode message raw directly instead
msg_raw = msg.as_string().encode()
smtp.sendmail(
forward_email.reply_email,
user_email,
msg_raw,
envelope.mail_options,
envelope.rcpt_options,
)
# smtp.send_message(
# msg,
# from_addr=forward_email.reply_email,
# to_addrs=[user_email], # user personal email
# mail_options=envelope.mail_options,
# rcpt_options=envelope.rcpt_options,
# )
else:
LOG.d("%s is disabled, do not forward", gen_email)
forward_log.blocked = True
db.session.commit()
return "250 Message accepted for delivery"
def handle_reply(self, envelope, smtp, msg: EmailMessage) -> str:
reply_email = envelope.rcpt_tos[0]
# reply_email must end with EMAIL_DOMAIN
if not reply_email.endswith(EMAIL_DOMAIN):
LOG.error(f"Reply email {reply_email} has wrong domain")
return "550 wrong reply email"
forward_email = ForwardEmail.get_by(reply_email=reply_email)
alias: str = forward_email.gen_email.email
notify_admin(f"Reply phase used by user: {forward_email.gen_email.user.email} ")
# todo: add DKIM-Signature for custom domain
# remove DKIM-Signature for custom domain
if not alias.endswith(EMAIL_DOMAIN) and msg["DKIM-Signature"]:
LOG.d(
"Remove DKIM-Signature %s for custom-domain alias %s",
msg["DKIM-Signature"],
alias,
)
del msg["DKIM-Signature"]
# email seems to come from alias
msg.replace_header("From", alias)
msg.replace_header("To", forward_email.website_email)
# add List-Unsubscribe header
unsubscribe_link = f"{URL}/dashboard/unsubscribe/{forward_email.gen_email_id}"
add_or_replace_header(msg, "List-Unsubscribe", f"<{unsubscribe_link}>")
add_or_replace_header(
msg, "List-Unsubscribe-Post", "List-Unsubscribe=One-Click"
)
LOG.d(
"send email from %s to %s, mail_options:%s,rcpt_options:%s",
alias,
forward_email.website_email,
envelope.mail_options,
envelope.rcpt_options,
)
msg_raw = msg.as_string().encode()
smtp.sendmail(
alias,
forward_email.website_email,
msg_raw,
envelope.mail_options,
envelope.rcpt_options,
)
ForwardEmailLog.create(forward_id=forward_email.id, is_reply=True)
db.session.commit()
return "250 Message accepted for delivery"
def add_or_replace_header(msg: EmailMessage, header: str, value: str):
try:
msg.add_header(header, value)
except ValueError:
# the header exists already
msg.replace_header(header, value)
def get_email_name(email_from):
"""parse email from header and return the name part
First Last <ab@cd.com> -> First Last
ab@cd.com -> ""
"""
if "<" in email_from:
return email_from[: email_from.find("<")].strip()
return ""
def get_email_part(email_from):
"""parse email from header and return the email part
First Last <ab@cd.com> -> ab@cd.com
ab@cd.com -> ""
"""
if "<" in email_from:
return email_from[email_from.find("<") + 1 : email_from.find(">")].strip()
return email_from
if __name__ == "__main__":
controller = Controller(MailHandler(), hostname="0.0.0.0", port=20381)
controller.start()
LOG.d("Start mail controller %s %s", controller.hostname, controller.port)
while True:
time.sleep(2)
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