email handler: forward phase. Todo: reply phase

email_handler.py

@@ -0,0 +1,145 @@
+"""
+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
+
+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: srs@sl.co # managed by SRS
+    rcpt to: @real
+Header:
+    From: @website
+    To: alias@sl.co
+    Reply-to: special@sl.co # magic here
+
+And in the reply phase:
+Envelope:
+    mail from: srs@sl.co # managed by SRS
+    rcpt to: @website
+
+Header:
+    From: alias@sl.co # 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.parser import Parser
+from email.policy import default
+from smtplib import SMTP
+
+from aiosmtpd.controller import Controller
+
+from app.config import EMAIL_DOMAIN
+from app.extensions import db
+from app.log import LOG
+from app.models import GenEmail, ForwardEmail
+from app.utils import random_words
+
+
+def parse_srs_email(srs) -> str:
+    """
+    Parse srs0=8lgw=y6=outlook.com=abcd@mailsl.meo.ovh and return abcd@outlook.com
+    """
+    local_part = srs[: srs.find("@")]  # srs0=8lgw=y6=outlook.com=abcd
+    local_email_part = local_part[local_part.rfind("=") + 1 :]  # abcd
+
+    rest = local_part[: local_part.rfind("=")]  # srs0=8lgw=y6=outlook.com
+    domain_email_part = rest[rest.rfind("=") + 1 :]  # outlook.com
+
+    return f"{local_email_part}@{domain_email_part}"
+
+
+class MailHandler:
+    async def handle_RCPT(self, server, session, envelope, address, rcpt_options):
+        if not address.endswith(EMAIL_DOMAIN):
+            LOG.error(f"Not handle email  {address}")
+            return "550 not relaying to that domain"
+
+        envelope.rcpt_tos.append(address)
+
+        return "250 OK"
+
+    async def handle_DATA(self, server, session, envelope):
+        LOG.debug(">>> handle_DATA <<<")
+
+        LOG.debug("Mail from %s", envelope.mail_from)
+        LOG.debug("Rcpt to %s", envelope.rcpt_tos)
+        LOG.debug("Message data:\n")
+        message_data = envelope.content.decode("utf8", errors="replace")
+        LOG.debug(message_data)
+        LOG.debug("End of message")
+
+        client = SMTP("localhost", 25)
+        msg = Parser(policy=default).parsestr(message_data)
+
+        if not envelope.rcpt_tos[0].startswith("reply+"):  # Forward case
+            LOG.debug("Forward phase, add Reply-To header")
+            alias = envelope.rcpt_tos[0]  # alias@SL
+
+            gen_email = GenEmail.get_by(email=alias)
+            website_email = parse_srs_email(envelope.mail_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,
+                    reply_email=reply_email,
+                )
+                db.session.commit()
+
+            # add custom header
+            msg.add_header("X-SimpleLogin-Type", "Forward")
+            msg.add_header("Reply-To", forward_email.reply_email)
+
+            client.send_message(
+                msg,
+                from_addr=envelope.mail_from,
+                to_addrs=[gen_email.user.emai],  # user personal email
+                mail_options=envelope.mail_options,
+                rcpt_options=envelope.rcpt_options,
+            )
+        else:
+            LOG.debug("Reply phase")
+            # todo: parse alias from envelope.rcpt_tos, e.g. ['reply+abcd+nguyenkims+hotmail.com@mailsl.meo.ovh']
+            alias = "abcd"
+
+            # email seems to come from alias
+            msg.replace_header("From", f"{alias}{DOMAIN}")
+            msg.replace_header("To", FROM)
+
+            client.send_message(
+                msg,
+                from_addr=f"{alias}{DOMAIN}",
+                to_addrs=[FROM],
+                mail_options=envelope.mail_options,
+                rcpt_options=envelope.rcpt_options,
+            )
+
+        return "250 Message accepted for delivery"
+
+
+controller = Controller(MailHandler(), hostname="localhost", port=20381)
+
+controller.start()
+print(">>", controller.hostname, controller.port)
+
+while True:
+    time.sleep(10)

tests/test_email_handler.py

@@ -0,0 +1,5 @@
+from email_handler import parse_srs_email
+
+
+def test_parse_srs_email():
+    assert parse_srs_email("srs0=8lgw=y6=outlook.com=abcd@sl.co") == "abcd@outlook.com"