diff --git a/docs/api-reference.md b/docs/api-reference.md
index b5b36fa..f5bb297 100644
--- a/docs/api-reference.md
+++ b/docs/api-reference.md
@@ -666,6 +666,11 @@ Body:
 
 Response: `204`
 
+Errors:
+
+- `404` - user with this email was not found.
+- `409` - contact cannot be added because a block relation exists.
+
 ### DELETE `/api/v1/users/{user_id}/contacts`
 
 Auth required.  
diff --git a/docs/core-checklist-status.md b/docs/core-checklist-status.md
index ba6d603..6a14cc0 100644
--- a/docs/core-checklist-status.md
+++ b/docs/core-checklist-status.md
@@ -10,7 +10,7 @@ Legend:
 1. Account - `PARTIAL` (email auth, JWT, refresh, logout, reset; sessions exist, full UX still improving)
 2. User Profile - `DONE` (username, name, avatar, bio, update)
 3. User Status - `PARTIAL` (online/last seen/offline; "recently" heuristic limited)
-4. Contacts - `PARTIAL` (list/search/add/remove/block/unblock; `add by email` flow covered by integration tests; UX moved to menu)
+4. Contacts - `PARTIAL` (list/search/add/remove/block/unblock; `add by email` flow covered by integration tests including `success/not found/blocked conflict`; UX moved to menu)
 5. Chat List - `DONE` (all/pinned/archive/sort/unread)
 6. Chat Types - `DONE` (private/group/channel)
 7. Chat Creation - `DONE` (private/group/channel)
diff --git a/tests/test_chat_message_flow.py b/tests/test_chat_message_flow.py
index 8ce0451..b860845 100644
--- a/tests/test_chat_message_flow.py
+++ b/tests/test_chat_message_flow.py
@@ -659,6 +659,27 @@ async def test_add_contact_by_email_success_and_not_found(client, db_session):
     assert add_missing_contact.status_code == 404
 
 
+async def test_add_contact_by_email_blocked_conflict(client, db_session):
+    owner = await _create_verified_user(client, db_session, "contact_email_block_owner@example.com", "contact_email_block_owner", "strongpass123")
+    target = await _create_verified_user(client, db_session, "contact_email_block_target@example.com", "contact_email_block_target", "strongpass123")
+
+    me_owner = await client.get("/api/v1/auth/me", headers={"Authorization": f"Bearer {owner['access_token']}"})
+    owner_id = me_owner.json()["id"]
+
+    block_owner = await client.post(
+        f"/api/v1/users/{owner_id}/block",
+        headers={"Authorization": f"Bearer {target['access_token']}"},
+    )
+    assert block_owner.status_code == 204
+
+    add_contact_blocked = await client.post(
+        "/api/v1/users/contacts/by-email",
+        headers={"Authorization": f"Bearer {owner['access_token']}"},
+        json={"email": "contact_email_block_target@example.com"},
+    )
+    assert add_contact_blocked.status_code == 409
+
+
 async def test_avatar_privacy_hidden_from_other_users_search(client, db_session):
     owner = await _create_verified_user(client, db_session, "avatar_owner@example.com", "avatar_owner", "strongpass123")
     viewer = await _create_verified_user(client, db_session, "avatar_viewer@example.com", "avatar_viewer", "strongpass123")