Postmark: Add metadata support

Closes #114

CHANGELOG.rst

@@ -40,6 +40,12 @@ Breaking changes
 *  **SendGrid:** Remove the legacy SendGrid *v2* EmailBackend
    (Anymail has defaulted to SendGrid's newer v3 API since Anymail v0.8.)
 
+Features
+~~~~~~~~
+
+* **Postmark:** Add support for Anymail's normalized `metadata` in sending
+  and webhooks.
+
 Fixes
 ~~~~~
 

anymail/backends/postmark.py

@@ -178,8 +178,8 @@ class PostmarkPayload(RequestsPayload):
                 self.make_attachment(attachment) for attachment in attachments
             ]
 
-    # Postmark doesn't support metadata
-    # def set_metadata(self, metadata):
+    def set_metadata(self, metadata):
+        self.data["Metadata"] = metadata
 
     # Postmark doesn't support delayed sending
     # def set_send_at(self, send_at):

anymail/webhooks/postmark.py

@@ -102,6 +102,7 @@ class PostmarkTrackingWebhookView(PostmarkBaseWebhookView):
         except KeyError:
             event_id = None
 
+        metadata = esp_event.get('Metadata', {})
         try:
             tags = [esp_event['Tag']]
         except KeyError:
@@ -113,6 +114,7 @@ class PostmarkTrackingWebhookView(PostmarkBaseWebhookView):
             event_id=event_id,
             event_type=event_type,
             message_id=esp_event.get('MessageID', None),
+            metadata=metadata,
             mta_response=esp_event.get('Details', None),
             recipient=recipient,
             reject_reason=reject_reason,

docs/esps/postmark.rst

@@ -100,10 +100,6 @@ see :ref:`unsupported-features`.
   if you've enabled :setting:`ANYMAIL_IGNORE_UNSUPPORTED_FEATURES`,
   Anymail will use only the first tag.
 
-**No metadata**
-  Postmark does not support attaching :attr:`~anymail.message.AnymailMessage.metadata`
-  to messages.
-
 **No delayed sending**
   Postmark does not support :attr:`~anymail.message.AnymailMessage.send_at`.
 

tests/test_postmark_backend.py

@@ -330,8 +330,9 @@ class PostmarkBackendAnymailFeatureTests(PostmarkBackendMockAPITestCase):
 
     def test_metadata(self):
         self.message.metadata = {'user_id': "12345", 'items': 6}
-        with self.assertRaisesMessage(AnymailUnsupportedFeature, 'metadata'):
-            self.message.send()
+        self.message.send()
+        data = self.get_api_call_json()
+        self.assertEqual(data['Metadata'], {'user_id': "12345", 'items': 6})
 
     def test_send_at(self):
         self.message.send_at = 1651820889  # 2022-05-06 07:08:09 UTC
@@ -403,6 +404,7 @@ class PostmarkBackendAnymailFeatureTests(PostmarkBackendMockAPITestCase):
         """
         self.message.send()
         data = self.get_api_call_json()
+        self.assertNotIn('Metadata', data)
         self.assertNotIn('Tag', data)
         self.assertNotIn('TemplateId', data)
         self.assertNotIn('TemplateModel', data)

tests/test_postmark_integration.py

@@ -51,7 +51,8 @@ class PostmarkBackendIntegrationTests(SimpleTestCase, AnymailTestMixin):
             reply_to=["reply1@example.com", "Reply 2 <reply2@example.com>"],
             headers={"X-Anymail-Test": "value"},
 
-            # no metadata, send_at, track_clicks support
+            # no send_at, track_clicks support
+            metadata={"meta1": "simple string", "meta2": 2},
             tags=["tag 1"],  # max one tag
             track_opens=True,
             track_clicks=True,

tests/test_postmark_webhooks.py

@@ -66,6 +66,10 @@ class PostmarkDeliveryTestCase(WebhookTestCase):
             "MessageID": "883953f4-6105-42a2-a16a-77a8eac79483",
             "Recipient": "recipient@example.com",
             "Tag": "welcome-email",
+            "Metadata": {
+                "cohort": "2014-08-A",
+                "userid": "12345",  # Postmark metadata is always converted to string
+            },
             "DeliveredAt": "2014-08-01T13:28:10.2735393-04:00",
             "Details": "Test delivery webhook details"
         }
@@ -83,7 +87,7 @@ class PostmarkDeliveryTestCase(WebhookTestCase):
         self.assertEqual(event.message_id, "883953f4-6105-42a2-a16a-77a8eac79483")
         self.assertEqual(event.recipient, "recipient@example.com")
         self.assertEqual(event.tags, ["welcome-email"])
-        self.assertEqual(event.metadata, {})
+        self.assertEqual(event.metadata, {"cohort": "2014-08-A", "userid": "12345"})
 
     def test_open_event(self):
         raw_event = {