use VERP for transactional email: remove SENDER, SENDER_DIR

app/config.py

@@ -60,6 +60,17 @@ BOUNCE_PREFIX = os.environ.get("BOUNCE_PREFIX") or "bounce+"
 BOUNCE_SUFFIX = os.environ.get("BOUNCE_SUFFIX") or f"+@{EMAIL_DOMAIN}"
 BOUNCE_EMAIL = BOUNCE_PREFIX + "{}" + BOUNCE_SUFFIX
 
+# VERP for transactional email: mail_from set to BOUNCE_PREFIX + email_log.id + BOUNCE_SUFFIX
+TRANSACTIONAL_BOUNCE_PREFIX = (
+    os.environ.get("TRANSACTIONAL_BOUNCE_PREFIX") or "transactional+"
+)
+TRANSACTIONAL_BOUNCE_SUFFIX = (
+    os.environ.get("TRANSACTIONAL_BOUNCE_SUFFIX") or f"+@{EMAIL_DOMAIN}"
+)
+TRANSACTIONAL_BOUNCE_EMAIL = (
+    TRANSACTIONAL_BOUNCE_PREFIX + "{}" + TRANSACTIONAL_BOUNCE_SUFFIX
+)
+
 try:
     MAX_NB_EMAIL_FREE_PLAN = int(os.environ["MAX_NB_EMAIL_FREE_PLAN"])
 except Exception:
@@ -69,12 +80,6 @@ except Exception:
 # maximum number of directory a premium user can create
 MAX_NB_DIRECTORY = 50
 
-# transactional email sender
-SENDER = os.environ.get("SENDER")
-
-# the directory to store bounce emails
-SENDER_DIR = os.environ.get("SENDER_DIR")
-
 ENFORCE_SPF = "ENFORCE_SPF" in os.environ
 
 # allow to override postfix server locally

app/dashboard/views/directory.py

@@ -120,7 +120,13 @@ def directory():
 
                 if Directory.get_by(name=new_dir_name):
                     flash(f"{new_dir_name} already added", "warning")
-                elif new_dir_name in ("reply", "ra", "bounces", "bounce"):
+                elif new_dir_name in (
+                    "reply",
+                    "ra",
+                    "bounces",
+                    "bounce",
+                    "transactional",
+                ):
                     flash(
                         "this directory name is reserved, please choose another name",
                         "warning",

app/email_utils.py

@@ -32,11 +32,11 @@ from app.config import (
     DISPOSABLE_EMAIL_DOMAINS,
     MAX_ALERT_24H,
     POSTFIX_PORT,
-    SENDER,
     URL,
     LANDING_PAGE_URL,
     EMAIL_DOMAIN,
     ALERT_DIRECTORY_DISABLED_ALIAS_CREATION,
+    TRANSACTIONAL_BOUNCE_EMAIL,
 )
 from app.dns_utils import get_mx_domains
 from app.extensions import db
@@ -50,6 +50,7 @@ from app.models import (
     Contact,
     Alias,
     EmailLog,
+    TransactionalEmail,
 )
 from app.utils import (
     random_string,
@@ -230,6 +231,7 @@ def send_email(
     unsubscribe_link=None,
     unsubscribe_via_email=False,
 ):
+    to_email = sanitize_email(to_email)
     if NOT_SEND_EMAIL:
         LOG.d(
             "send email with subject '%s' to '%s', plaintext: %s",
@@ -277,10 +279,13 @@ def send_email(
     add_dkim_signature(msg, email_domain)
 
     msg_raw = to_bytes(msg)
-    if SENDER:
-        smtp.sendmail(SENDER, to_email, msg_raw)
-    else:
-        smtp.sendmail(SUPPORT_EMAIL, to_email, msg_raw)
+
+    transaction = TransactionalEmail.get_by(email=to_email)
+    if not transaction:
+        transaction = TransactionalEmail.create(email=to_email, commit=True)
+
+    # use a different envelope sender for each transactional email (aka VERP)
+    smtp.sendmail(TRANSACTIONAL_BOUNCE_EMAIL.format(transaction.id), to_email, msg_raw)
 
 
 def send_email_with_rate_control(

app/models.py

@@ -2114,8 +2114,7 @@ class Metric(db.Model, ModelMixin):
 
 
 class Bounce(db.Model, ModelMixin):
-    """Record all bounces. Deleted after 7 days
-    """
+    """Record all bounces. Deleted after 7 days"""
 
     email = db.Column(db.String(256), nullable=False, index=True)
 

email_handler.py

@@ -68,8 +68,6 @@ from app.config import (
     ALERT_SPAM_EMAIL,
     ALERT_SPF,
     POSTFIX_PORT,
-    SENDER,
-    SENDER_DIR,
     SPAMASSASSIN_HOST,
     MAX_SPAM_SCORE,
     MAX_REPLY_PHASE_SPAM_SCORE,
@@ -81,6 +79,8 @@ from app.config import (
     BOUNCE_EMAIL,
     BOUNCE_PREFIX,
     BOUNCE_SUFFIX,
+    TRANSACTIONAL_BOUNCE_PREFIX,
+    TRANSACTIONAL_BOUNCE_SUFFIX,
 )
 from app.email_utils import (
     send_email,
@@ -1502,26 +1502,21 @@ def handle_unsubscribe_user(user_id: int, mail_from: str) -> str:
     return "250 Unsubscribe request accepted"
 
 
-def handle_sender_email(envelope: Envelope):
-    filename = (
-        arrow.now().format("YYYY-MM-DD_HH-mm-ss") + "_" + random_string(10) + ".eml"
-    )
-    filepath = os.path.join(SENDER_DIR, filename)
+def handle_transactional_bounce(envelope: Envelope, rcpt_to):
+    LOG.d("handle transactional bounce sent to %s", rcpt_to)
 
-    with open(filepath, "wb") as f:
-        f.write(envelope.original_content)
+    # parse the TransactionalEmail
+    transactional_id = parse_id_from_bounce(rcpt_to)
+    transactional = TransactionalEmail.get(transactional_id)
 
-    LOG.d("Write email to sender at %s", filepath)
-
-    msg = email.message_from_bytes(envelope.original_content)
-    orig = get_orig_message_from_bounce(msg)
-    if orig:
-        LOG.warning(
-            "Original message %s -> %s saved at %s", orig["From"], orig["To"], filepath
+    if transactional:
+        LOG.info("Create bounce for %s", transactional.email)
+        Bounce.create(email=transactional.email, commit=True)
+    else:
+        LOG.exception(
+            "Cannot find transactional email for %s %s", transactional_id, rcpt_to
         )
 
-    return "250 email to sender accepted"
-
 
 def handle(envelope: Envelope) -> str:
     """Return SMTP status"""
@@ -1538,9 +1533,14 @@ def handle(envelope: Envelope) -> str:
         return handle_unsubscribe(envelope)
 
     # emails sent to sender. Probably bounce emails
-    if SENDER and rcpt_tos == [SENDER]:
+    if (
+        len(rcpt_tos) == 1
+        and rcpt_tos[0].startswith(TRANSACTIONAL_BOUNCE_PREFIX)
+        and rcpt_tos[0].endswith(TRANSACTIONAL_BOUNCE_SUFFIX)
+    ):
         LOG.d("Handle email sent to sender from %s", mail_from)
-        return handle_sender_email(envelope)
+        handle_transactional_bounce(envelope, rcpt_tos[0])
+        return "250 bounce handled"
 
     if (
         len(rcpt_tos) == 1

example.env

@@ -36,8 +36,6 @@ PREMIUM_ALIAS_DOMAINS=["premium.com"]
 # transactional email is sent from this email address
 SUPPORT_EMAIL=support@sl.local
 SUPPORT_NAME=Son from SimpleLogin
-# in case sender is different than SUPPORT_EMAIL
-SENDER=sender@sl.local
 
 # To use VERP
 # prefix must end with + and suffix must start with +
@@ -45,9 +43,6 @@ SENDER=sender@sl.local
 # BOUNCE_SUFFIX = "+@sl.local"
 
 
-# all emails sent to sender are stored in this folder
-SENDER_DIR=/tmp
-
 # to receive general stats.
 # ADMIN_EMAIL=admin@sl.local