[ENG-12046] Fix sendgrid bulk personalization

osf/email/__init__.py

@@ -238,7 +238,33 @@ def send_email_over_smtp(to_email, notification_type, context, email_context):
             email.attach(attachment_name, attachment_content)
     email.send()
 
-def send_email_with_send_grid(to_addr, notification_type, context, email_context=None):
+def _build_sendgrid_personalizations(to_list, email_context=None, is_multiple=False):
+    """Build SendGrid personalizations for one shared message or one message per recipient.
+
+    When ``is_multiple`` is True, each address gets its own personalization (separate
+    delivery; recipients do not see each other). CC/BCC are omitted in that mode to
+    avoid duplicating copies per recipient.
+    """
+    email_context = email_context or {}
+
+    if is_multiple:
+        # If we attached the same CC/BCC to every personalization in is_multiple mode,
+        # a batch of N recipients would produce N separate emails each including that CC
+        # so the CC address would get N copies of the same message
+        # TODO: decide if it's safe to add the CC/BCC to each personalization
+        return [{'to': [{'email': addr}]} for addr in to_list]
+
+    personalization = {'to': [{'email': addr} for addr in to_list]}
+    cc_addr = email_context.get('cc_addr')
+    if cc_addr:
+        personalization['cc'] = [{'email': a} for a in ([cc_addr] if isinstance(cc_addr, str) else cc_addr)]
+    bcc_addr = email_context.get('bcc_addr')
+    if bcc_addr:
+        personalization['bcc'] = [{'email': a} for a in ([bcc_addr] if isinstance(bcc_addr, str) else bcc_addr)]
+    return [personalization]
+
+
+def send_email_with_send_grid(to_addr, notification_type, context, email_context=None, *, is_multiple=False):
 
     email_context = email_context or {}
     to_list = [to_addr] if isinstance(to_addr, str) else [a for a in (to_addr or []) if a]
@@ -256,18 +282,12 @@ def send_email_with_send_grid(to_addr, notification_type, context, email_context
     subject_tpl = getattr(notification_type, 'subject', None)
     subject = subject_tpl.format(**context) if subject_tpl else f'Notification: {getattr(notification_type, "name", "OSF")}'
 
-    personalization = {'to': [{'email': addr} for addr in to_list]}
-    cc_addr = email_context.get('cc_addr')
-    if cc_addr:
-        personalization['cc'] = [{'email': a} for a in ([cc_addr] if isinstance(cc_addr, str) else cc_addr)]
-    bcc_addr = email_context.get('bcc_addr')
-    if bcc_addr:
-        personalization['bcc'] = [{'email': a} for a in ([bcc_addr] if isinstance(bcc_addr, str) else bcc_addr)]
-
     payload = {
         'from': {'email': from_email},
         'subject': subject,
-        'personalizations': [personalization],
+        'personalizations': _build_sendgrid_personalizations(
+            to_list, email_context=email_context, is_multiple=is_multiple
+        ),
         'content': [
             {'type': 'text/html', 'value': html},
         ],

osf/email/notification_campaign.py

@@ -383,7 +383,12 @@ def send_campaign_batch(
         # NOTE: sendgrid bulk send feature has not been fully implemented and tested
         recipient_emails = list(valid_emails_qs.values_list('recipient_address', flat=True))
         try:
-            send_email_with_send_grid(to_addr=recipient_emails, notification_type=notification_type, context=context)
+            send_email_with_send_grid(
+                to_addr=recipient_emails,
+                notification_type=notification_type,
+                context=context,
+                is_multiple=True,
+            )
             valid_emails_qs.update(status=NotificationCampaignRecipientStatus.SENT, error_message=None)
         except Exception as exc:
             message = (f'[Notification Campaign #{campaign_id}] ERROR: '

osf_tests/test_notification_campaign.py

@@ -6,6 +6,7 @@
 from django.utils import timezone
 from django.db.models import Q
 
+from osf.email import _build_sendgrid_personalizations
 from osf.email.notification_campaign import (
     create_campaign_recipients,
     get_campaign_recipient_batches,
@@ -573,10 +574,33 @@ def test_send_campaign_batch_sendgrid_bulk_success(self, mock_sendgrid, running_
         recipient.refresh_from_db()
         running_campaign.refresh_from_db()
         mock_sendgrid.assert_called_once()
+        assert mock_sendgrid.call_args.kwargs.get('is_multiple') is True
         assert recipient.status == NotificationCampaignRecipientStatus.SENT
         assert running_campaign.sent_count == 1
         assert running_campaign.failed_count == 0
 
+    def test_build_sendgrid_personalizations_shared_to_list(self):
+        personalizations = _build_sendgrid_personalizations(
+            ['a@example.com', 'b@example.com'],
+            is_multiple=False,
+        )
+        assert personalizations == [{
+            'to': [
+                {'email': 'a@example.com'},
+                {'email': 'b@example.com'},
+            ],
+        }]
+
+    def test_build_sendgrid_personalizations_one_per_recipient(self):
+        personalizations = _build_sendgrid_personalizations(
+            ['a@example.com', 'b@example.com'],
+            is_multiple=True,
+        )
+        assert personalizations == [
+            {'to': [{'email': 'a@example.com'}]},
+            {'to': [{'email': 'b@example.com'}]},
+        ]
+
     @mock.patch(
         'osf.email.notification_campaign.send_email_with_send_grid',
         side_effect=Exception('bulk failed'),