send_email: Add function to generate tokenized noreply in FromAddress.

zerver/lib/send_email.py

@@ -15,6 +15,7 @@ import os
 from typing import Any, Dict, Iterable, List, Mapping, Optional
 
 from zerver.lib.logging_util import log_to_file
+from confirmation.models import generate_key
 
 ## Logging setup ##
 
@@ -25,6 +26,13 @@ class FromAddress:
     SUPPORT = parseaddr(settings.ZULIP_ADMINISTRATOR)[1]
     NOREPLY = parseaddr(settings.NOREPLY_EMAIL_ADDRESS)[1]
 
+    # Generates an unpredictable noreply address.
+    @staticmethod
+    def tokenized_no_reply_address() -> str:
+        if settings.ADD_TOKENS_TO_NOREPLY_ADDRESS:
+            return parseaddr(settings.TOKENIZED_NOREPLY_EMAIL_ADDRESS)[1].format(token=generate_key())
+        return FromAddress.NOREPLY
+
 def build_email(template_prefix: str, to_user_id: Optional[int]=None,
                 to_email: Optional[str]=None, from_name: Optional[str]=None,
                 from_address: Optional[str]=None, reply_to_email: Optional[str]=None,

zerver/lib/test_classes.py

@@ -104,6 +104,7 @@ class ZulipTestCase(TestCase):
     '''
     DEFAULT_SUBDOMAIN = "zulip"
     DEFAULT_REALM = Realm.objects.get(string_id='zulip')
+    TOKENIZED_NOREPLY_REGEX = settings.TOKENIZED_NOREPLY_EMAIL_ADDRESS.format(token="[a-z0-9_]{24}")
 
     def set_http_host(self, kwargs: Dict[str, Any]) -> None:
         if 'subdomain' in kwargs:

zerver/tests/test_signup.py

@@ -2937,6 +2937,13 @@ class FollowupEmailTest(ZulipTestCase):
         user_profile.date_joined = datetime.datetime(2018, 1, 5, 1, 0, 0, 0, pytz.UTC)
         self.assertEqual(followup_day2_email_delay(user_profile), datetime.timedelta(days=1, hours=-1))
 
+class NoReplyEmailTest(ZulipTestCase):
+    def test_noreply_email_address(self) -> None:
+        self.assertTrue(re.search(self.TOKENIZED_NOREPLY_REGEX, FromAddress.tokenized_no_reply_address()))
+
+        with self.settings(ADD_TOKENS_TO_NOREPLY_ADDRESS=False):
+            self.assertEqual(FromAddress.tokenized_no_reply_address(), "noreply@testserver")
+
 class TwoFactorAuthTest(ZulipTestCase):
     @patch('two_factor.models.totp')
     def test_two_factor_login(self, mock_totp):

zproject/settings.py

@@ -122,6 +122,8 @@ DEFAULT_SETTINGS = {
 
     # Basic email settings
     'NOREPLY_EMAIL_ADDRESS': "noreply@" + EXTERNAL_HOST.split(":")[0],
+    'ADD_TOKENS_TO_NOREPLY_ADDRESS': True,
+    'TOKENIZED_NOREPLY_EMAIL_ADDRESS': "noreply-{token}@" + EXTERNAL_HOST.split(":")[0],
     'PHYSICAL_ADDRESS': '',
 
     # SMTP settings