""" 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 Message 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 ( get_email_name, get_email_part, send_email, add_dkim_signature, get_email_domain_part, add_or_replace_header, delete_header, ) from app.extensions import db from app.log import LOG from app.models import GenEmail, ForwardEmail, ForwardEmailLog, CustomDomain from app.utils import random_string 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) rcpt_to = envelope.rcpt_tos[0].lower() # Reply case # reply+ or ra+ (reverse-alias) prefix if rcpt_to.startswith("reply+") or rcpt_to.startswith("ra+"): LOG.debug("Reply phase") app = new_app() with app.app_context(): return self.handle_reply(envelope, smtp, msg) else: # Forward case LOG.debug("Forward phase") app = new_app() with app.app_context(): return self.handle_forward(envelope, smtp, msg) def handle_forward(self, envelope, smtp: SMTP, msg: Message) -> str: """return *status_code message*""" alias = envelope.rcpt_tos[0].lower() # alias@SL gen_email = GenEmail.get_by(email=alias) if not gen_email: LOG.d("alias %s not exist", alias) # check if alias is custom-domain alias and if the custom-domain has catch-all enabled alias_domain = get_email_domain_part(alias) custom_domain = CustomDomain.get_by(domain=alias_domain) if custom_domain and custom_domain.catch_all: LOG.d("create alias %s for domain %s", alias, custom_domain) gen_email = GenEmail.create( email=alias, user_id=custom_domain.user_id, custom_domain_id=custom_domain.id, automatic_creation=True, ) db.session.commit() else: 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, ) # generate a reply_email, make sure it is unique # not use while to avoid infinite loop for _ in range(1000): reply_email = f"reply+{random_string(30)}@{EMAIL_DOMAIN}" if not ForwardEmail.get_by(reply_email=reply_email): break 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 delete_header(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" ) add_dkim_signature(msg, EMAIL_DOMAIN) LOG.d( "Forward mail from %s to %s, mail_options %s, rcpt_options %s ", website_email, user_email, 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, ) 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: SMTP, msg: Message) -> str: reply_email = envelope.rcpt_tos[0].lower() # 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 # alias must end with EMAIL_DOMAIN or custom-domain alias_domain = alias[alias.find("@") + 1 :] if alias_domain != EMAIL_DOMAIN: if not CustomDomain.get_by(domain=alias_domain): return "550 alias unknown by SimpleLogin" user_email = forward_email.gen_email.user.email if envelope.mail_from.lower() != user_email.lower(): LOG.error( f"Reply email can only be used by user email. Actual mail_from: %s. User email %s", envelope.mail_from, user_email, ) send_email( envelope.mail_from, f"Your email ({envelope.mail_from}) is not allowed to send email to {reply_email}", "", "", ) return "450 ignored" delete_header(msg, "DKIM-Signature") # the email comes from alias msg.replace_header("From", alias) # some email providers like ProtonMail adds automatically the Reply-To field # make sure to delete it delete_header(msg, "Reply-To") 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" ) # Received-SPF is injected by postfix-policyd-spf-python can reveal user original email delete_header(msg, "Received-SPF") 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, ) if alias_domain == EMAIL_DOMAIN: add_dkim_signature(msg, EMAIL_DOMAIN) # add DKIM-Signature for non-custom-domain alias else: custom_domain: CustomDomain = CustomDomain.get_by(domain=alias_domain) if custom_domain.dkim_verified: add_dkim_signature(msg, alias_domain) 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" 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)