register_remote_server: Check for NS records, now just A/AAAA.

We shouldn't declare that the domain doesn't exist, if it has a valid
NS record but no A/AAAA.

zerver/tests/test_push_notifications.py

@@ -2677,7 +2677,16 @@ class PushBouncerSignupTest(ZulipTestCase):
         request["contact_email"] = "admin@zulip.com"
         with mock.patch("zilencer.views.dns_resolver.Resolver") as resolver:
             resolver.return_value.resolve.side_effect = DNSNoAnswer
-            resolver.return_value.resolve_name.return_value = ["whee"]
+            resolver.return_value.resolve_name.return_value = ["A/AAAA response"]
+            result = self.client_post("/api/v1/remotes/server/register", request)
+            self.assert_json_error(
+                result,
+                "Invalid server administrator email address: zulip.com is invalid because it does not have any MX records",
+            )
+
+        with mock.patch("zilencer.views.dns_resolver.Resolver") as resolver:
+            resolver.return_value.resolve.side_effect = [DNSNoAnswer, "NS response"]
+            resolver.return_value.resolve_name.side_effect = DNSNoAnswer
             result = self.client_post("/api/v1/remotes/server/register", request)
             self.assert_json_error(
                 result,
@@ -2693,7 +2702,7 @@ class PushBouncerSignupTest(ZulipTestCase):
             )
 
         with mock.patch("zilencer.views.dns_resolver.Resolver") as resolver:
-            resolver.return_value.resolve.return_value = ["whee"]
+            resolver.return_value.resolve.return_value = ["MX response"]
             result = self.client_post("/api/v1/remotes/server/register", request)
             self.assert_json_success(result)
 

zilencer/views.py

@@ -266,9 +266,17 @@ def register_remote_server(
                 )
             )
         except DNSException:
-            raise ServerAdminEmailError(
+            try:
-                _("{domain} does not exist").format(domain=contact_email_domain)
+                resolver.resolve(contact_email_domain, rdtype="NS")
-            )
+                raise ServerAdminEmailError(
+                    _("{domain} is invalid because it does not have any MX records").format(
+                        domain=contact_email_domain
+                    )
+                )
+            except DNSException:
+                raise ServerAdminEmailError(
+                    _("{domain} does not exist").format(domain=contact_email_domain)
+                )
 
     try:
         validate_uuid(zulip_org_id)