diff --git a/products/messaging/backend/services/transactional_email.py b/products/messaging/backend/services/transactional_email.py
index af0dfa649a41..85ec16565841 100644
--- a/products/messaging/backend/services/transactional_email.py
+++ b/products/messaging/backend/services/transactional_email.py
@@ -527,7 +527,12 @@ def _code_send_sender(team_id: int, address: str | None) -> dict[str, Any]:
         if address:
             raise NamedSenderNotVerified(f"No verified sender in this project can send from `{email}`.") from e
         raise SenderNotVerified("The project has no verified default email sender.") from e
-    return {"integrationId": sender.integration_id, "email": sender.email, "name": sender.name}
+    return {
+        "integrationId": sender.integration_id,
+        "email": sender.email,
+        "name": sender.name,
+        "isDefault": not address,
+    }
 
 
 def _without_empty(fields: dict[str, Any]) -> dict[str, Any]:
diff --git a/products/messaging/backend/tests/api/test_transactional_email.py b/products/messaging/backend/tests/api/test_transactional_email.py
index 7bdc2552efbd..423b0450e79f 100644
--- a/products/messaging/backend/tests/api/test_transactional_email.py
+++ b/products/messaging/backend/tests/api/test_transactional_email.py
@@ -428,7 +428,7 @@ def test_a_code_send_goes_out_as_is_under_the_keys_workflow(
             "variables": {},
             "send": {
                 "content": {"subject": "Welcome, Jane", "html": "<p>Hi Jane</p>", "text": "Hi Jane"},
-                "from": {"integrationId": self.sender.id},
+                "from": {"integrationId": self.sender.id, "isDefault": True},
                 "tracking": {"captureEngagement": True},
             },
         }
@@ -471,13 +471,18 @@ def test_a_code_send_makes_a_new_workflow_when_its_keys_workflow_was_deleted(sel
                 {"capture_engagement": False},
                 {
                     "content": {"subject": "Welcome, Jane", "html": "<p>Hi Jane</p>", "text": "Hi Jane"},
+                    "from": {"isDefault": True},
                     "tracking": {"captureEngagement": False},
                 },
             ),
             (
                 "text_only",
                 {"html": "", "text": "Hi"},
-                {"content": {"subject": "Welcome, Jane", "text": "Hi"}, "tracking": {"captureEngagement": True}},
+                {
+                    "content": {"subject": "Welcome, Jane", "text": "Hi"},
+                    "from": {"isDefault": True},
+                    "tracking": {"captureEngagement": True},
+                },
             ),
         ]
     )