Add filtermail

chatmail-pyinfra/src/chatmail/__init__.py

@@ -23,10 +23,6 @@ def _install_doveauth() -> None:
             src=doveauth_path.open("rb"),
             dest=remote_path,
         )
-        apt.packages(
-            name="apt install python3-pip",
-            packages="python3-pip",
-        )
         # Maybe if we introduce dependencies to the doveauth package at some point, we should not install doveauth
         # system-wide anymore. For now it's fine though.
         server.shell(
@@ -35,6 +31,48 @@ def _install_doveauth() -> None:
         )
 
 
+def _install_filtermail() -> None:
+    """Setup filtermail."""
+    filtermail_filename = "filtermail-0.1.tar.gz"
+    filtermail_path = importlib.resources.files(__package__).joinpath(
+        f"../../../filtermail/dist/{filtermail_filename}"
+    )
+    remote_path = f"/tmp/{filtermail_filename}"
+    if Path(str(filtermail_path)).exists():
+        files.put(
+            name="upload local filtermail build",
+            src=filtermail_path.open("rb"),
+            dest=remote_path,
+        )
+        apt.packages(
+            name="apt install python3-aiosmtpd",
+            packages="python3-aiosmtpd",
+        )
+
+        # --no-deps because aiosmtplib is installed with `apt`.
+        server.shell(
+            name="install local doveauth build with pip",
+            commands=[f"pip install --break-system-packages --no-deps {remote_path}"],
+        )
+
+        files.put(
+            src=importlib.resources.files(__package__)
+            .joinpath("../../../filtermail/filtermail.service")
+            .open("rb"),
+            dest="/etc/systemd/system/filtermail.service",
+            user="root",
+            group="root",
+            mode="644",
+        )
+        systemd.service(
+            name="Setup filtermail service",
+            service="filtermail.service",
+            running=True,
+            enabled=True,
+            restarted=True,
+        )
+
+
 def _configure_opendkim(domain: str, dkim_selector: str) -> bool:
     """Configures OpenDKIM"""
     need_restart = False
@@ -172,7 +210,12 @@ def deploy_chatmail(mail_domain: str, mail_server: str, dkim_selector: str) -> N
         ],
     )
 
+    apt.packages(
+        name="apt install python3-pip",
+        packages="python3-pip",
+    )
     _install_doveauth()
+    _install_filtermail()
     dovecot_need_restart = _configure_dovecot(mail_server)
     postfix_need_restart = _configure_postfix(mail_domain)
     opendkim_need_restart = _configure_opendkim(mail_domain, dkim_selector)

chatmail-pyinfra/src/chatmail/postfix/master.cf

@@ -28,6 +28,7 @@ submission inet n       -       y       -       -       smtpd
   -o smtpd_recipient_restrictions=
   -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
   -o milter_macro_daemon_name=ORIGINATING
+  -o content_filter=filter:unix:private/filtemail
 smtps     inet  n       -       y       -       -       smtpd
   -o syslog_name=postfix/smtps
   -o smtpd_tls_wrappermode=yes
@@ -42,6 +43,7 @@ smtps     inet  n       -       y       -       -       smtpd
   -o smtpd_recipient_restrictions=
   -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
   -o milter_macro_daemon_name=ORIGINATING
+  -o content_filter=filter:unix:private/filtermail
 #628       inet  n       -       y       -       -       qmqpd
 pickup    unix  n       -       y       60      1       pickup
 cleanup   unix  n       -       y       -       0       cleanup
@@ -70,3 +72,7 @@ lmtp      unix  -       -       y       -       -       lmtp
 anvil     unix  -       -       y       -       1       anvil
 scache    unix  -       -       y       -       1       scache
 postlog   unix-dgram n  -       n       -       1       postlogd
+filter    unix -        n       n       -       -       lmtp
+# Local SMTP server for reinjecting filered mail.
+localhost:10026 inet  n       -       n       -       10      smtpd
+        -o content_filter=

filtermail/filtermail.service

@@ -0,0 +1,10 @@
+[Unit]
+Description=Email filter for chatmail servers
+
+[Service]
+ExecStart=/usr/local/bin/filtermail
+Restart=always
+RestartSec=30
+
+[Install]
+WantedBy=multi-user.target

filtermail/pyproject.toml

@@ -0,0 +1,33 @@
+[build-system]
+requires = ["setuptools>=45"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "filtermail"
+version = "0.1"
+dependencies = [
+  "aiosmtpd"
+]
+
+[project.scripts]
+filtermail = "filtermail.filtermail:main"
+
+[tool.pytest.ini_options]
+addopts = "-v -ra --strict-markers"
+
+[tool.tox]
+legacy_tox_ini = """
+[tox]
+isolated_build = true
+envlist = lint
+
+[testenv:lint]
+skipdist = True
+skip_install = True
+deps =
+  ruff
+  black
+commands =
+  black --quiet --check --diff src/
+  ruff src/
+"""

filtermail/src/filtermail/filtermail.py

@@ -0,0 +1,85 @@
+#!/usr/bin/env python3
+import asyncio
+import logging
+
+from aiosmtpd.lmtp import LMTP
+from aiosmtpd.controller import UnixSocketController
+from smtplib import SMTP as SMTPClient
+
+
+def check_encrypted(envelope):
+    """https://xkcd.com/1181/"""
+    return "-----BEGIN PGP MESSAGE-----" in envelope.content.decode(
+        "utf8", errors="replace"
+    )
+
+
+class ExampleController(UnixSocketController):
+    def factory(self):
+        return LMTP(self.handler, **self.SMTP_kwargs)
+
+
+class ExampleHandler:
+    async def handle_RCPT(self, server, session, envelope, address, rcpt_options):
+        envelope.rcpt_tos.append(address)
+        return "250 OK"
+
+    async def handle_DATA(self, server, session, envelope):
+        logging.info("Processing DATA message from %s", envelope.mail_from)
+
+        valid_recipients = []
+
+        mail_encrypted = check_encrypted(envelope)
+
+        res = []
+        for recipient in envelope.rcpt_tos:
+            my_local_domain = envelope.mail_from.split("@")
+            if len(my_local_domain) != 2:
+                res += [f"500 Invalid from address <{envelope.mail_from}>"]
+                continue
+
+            if envelope.mail_from == recipient:
+                # Always allow sending emails to self.
+                valid_recipients += [recipient]
+                res += ["250 OK"]
+                continue
+
+            recipient_local_domain = recipient.split("@")
+            if len(recipient_local_domain) != 2:
+                res += [f"500 Invalid address <{recipient}>"]
+                continue
+
+            is_outgoing = recipient_local_domain[1] != my_local_domain[1]
+            if is_outgoing and not mail_encrypted:
+                res += ["500 Outgoing mail must be encrypted"]
+                continue
+
+            valid_recipients += [recipient]
+            res += ["250 OK"]
+
+        # Reinject the mail back into Postfix.
+        if valid_recipients:
+            logging.info("Reinjecting the mail")
+            client = SMTPClient("localhost", "10026")
+            client.sendmail(envelope.mail_from, valid_recipients, envelope.content)
+
+        return "\r\n".join(res)
+
+
+async def asyncmain(loop):
+    controller = ExampleController(
+        ExampleHandler(), unix_socket="/var/spool/postfix/private/filtermail"
+    )
+    controller.start()
+
+
+def main():
+    logging.basicConfig(level=logging.INFO)
+    loop = asyncio.new_event_loop()
+    asyncio.set_event_loop(loop)
+    loop.create_task(asyncmain(loop=loop))
+    loop.run_forever()
+
+
+if __name__ == "__main__":
+    main()

plan.txt

@@ -11,14 +11,12 @@
 4. automatic expiry of users that haven't logged in for N days
 
 
-## Postfix goals/steps
+## Filtermail
 
-1. block all outgoing mails with our own LMTP program
+1. Only allow (outgoing) mails if secure-join or autocrypt-pgp-encrypted format.
+   Currently only checks for "-----BEGIN PGP MESSAGE-----".
 
-2. only allow (outgoing) mails if secure-join or autocrypt-pgp-encrypted format
-   (probably via an lmtp service)
-
-3. basic outgoing send rate/limits (depending on "account-rating")
+2. basic outgoing send rate/limits (depending on "account-rating")
 
 
 ## online tests (first with plain python/pytest)

scripts/deploy.sh

@@ -1,7 +1,16 @@
 #!/usr/bin/env bash
 : ${CHATMAIL_DOMAIN:=c1.testrun.org}
 export CHATMAIL_DOMAIN
-cd doveauth
+
+pushd doveauth
 venv/bin/python3 -m build
-../chatmail-pyinfra/venv/bin/pyinfra --ssh-user root "$CHATMAIL_DOMAIN" ../deploy.py
-rm -r dist/
+popd
+
+pushd filtermail
+venv/bin/python3 -m build
+popd
+
+chatmail-pyinfra/venv/bin/pyinfra --ssh-user root "$CHATMAIL_DOMAIN" deploy.py
+
+#rm -r doveauth/dist/
+#rm -r filtermail/dist/

scripts/init.sh

@@ -10,3 +10,7 @@ doveauth/venv/bin/pip install -e doveauth
 
 python3 -m venv online-tests/venv
 online-tests/venv/bin/pip install pytest pytest-timeout pdbpp deltachat
+
+python3 -m venv filtermail/venv
+filtermail/venv/bin/pip install build
+filtermail/venv/bin/pip install -e filtermail